The Conversation: Predators, prey and moonlight singing: how phases of the Moon affect native wildlife

Image credits: Wes Mountain / The Conversation

By Euan Ritchie (Deakin University), Courtney Marneweck (Clemson University), and Grant Linley (Charles Sturt University).

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Humans have long been inspired and transfixed by the Moon, and as we’re discovering, moonlight can also change the behaviour of Australian wildlife.

A collection of recently published research has illuminated how certain behaviours of animals – including potoroos, wallabies and quolls – change with variation in ambient light, phases of the Moon and cloud cover.

One study found small mammals were more active on cloudy nights. Another found variation in moonlight led to differing amounts of species captured in non-lethal traps. And a study on willie wagtails found males just love singing on a full moon.

These findings are interesting from a natural history perspective. But they’ll also help ecologists and conservation scientists better locate and study nocturnal animals, and learn how artificial light pollution is likely changing where animals can live and how they behave.

Moonlit predator-prey games of hide and seek

Most of Australia’s mammals are nocturnal, and some smaller species are thought to use the cover of darkness to avoid the attention of hungry predators. However, there’s much we don’t know about such relationships, especially because it can be difficult to study these interactions in the wild.

In the relatively diverse mammal community at Mt Rothwell, Victoria, we examined how variation in ambient light affected species’ activity, and how this might influence species interactions. Mt Rothwell is a fenced conservation reserve free of feral cats and foxes, and with minimal light pollution.

Over two years, we surveyed the responses of predator and prey species to different light levels from full, half and new moon phases.

Potential prey species in our study included eastern barred and southern brown bandicoots, long-nosed potoroos, brushtailed rock-wallabies, and brushtail and common ringtail possums. Eastern and spotted-tailed quolls are their potential predators.

Just as we predicted, we found that while there does appear to be relationships between cloud cover, Moon phase and mammal activity, these interactions depend on the sizes and types of mammals involved.

Both predators and prey generally increased their activity in darker conditions.
Smaller, prey species increased their activity when cloud cover was higher, and predators increased their activity during the half and new moon phases.

This suggests their deadly game of hide and seek might intensify on darker nights. And prey might have to trade off foraging time to reduce their chances of becoming the evening meal.

What happens in the wild?

It’s important to acknowledge that studies in sanctuaries such as Mt Rothwell might not always reflect well what goes on in the wild, including in areas where introduced predators, such as feral cats and red foxes, are found.

Another recent study, this time of small mammals in the wilds of Victoria’s Mallee region, sheds further light on the situation. The authors tested if variation in weather and Moon phase affected the numbers of five small mammal species – Bolam’s mouse, common dunnart, house mouse, southern ningaui, and western pygmy possum – captured in pitfall traps.

Pitfall traps are long fences small animals can’t climb over or through, so follow along the side until they fall into a bucket dug in the ground. Ecologists typically use these traps to capture and measure animals and then return them to the wild, unharmed.

At more than 260 sites and over more than 50,000 trap nights, they found wind speed, temperature and moonlight influenced which species were caught and in what numbers.

For example, captures of a small native rodent, Bolam’s mouse, and carnivorous marsupial, southern ningaui, decreased with more moonlight, whereas captures of pygmy possums were higher with more moonlight.

Moonlight songbird serenades

Research from last month has shown even species normally active by day may change their behaviour and activity by night.

It’s not uncommon to hear bird song by night, including the quintessentially Aussie warbling of magpies. Using bioacoustic recorders and song detection software, these researchers show the willie wagtail – another of Australia’s most recogisable and loved birds – is also a nighttime singer, particularly during the breeding season.

While both male and female wagtails sing by day, it is the males that are most vocal by night. And it seems the males aren’t afraid of a little stage-lighting either, singing more with increasing moonlight, with performances peaking during full moons.

This work provides insight into the importance and potential role of nocturnal song for birds, such as mate attraction or territory defence, and helps us to better understand these behaviours more generally.

Moonlight affects wildlife conservation

These studies, and others, can help inform wildlife conservation, as practically speaking, ecological surveys must consider the relative brightness of nights during which work occurred.

Depending on when and where we venture out to collect information about species, and what methods we use (camera traps, spotlighting, and non-lethal trapping) we might have higher or lower chances of detecting certain species. And this might affect our insights into species and ecosystems, and how we manage them.

As dark skies become rarer in many places around the world, it also begs a big question. To what extent is all the artificial light pollution in our cities and peri-urban areas affecting wildlife and ecosystems?

Pipistrelle bats, for example, will be roughly half as active around well-lit bridges than unlit bridges. They’ll also keep further away from well-lit bridges, and fly faster when near them.

This means artificial light might reduce the amount and connectivity of habitat available to some bat species in urban areas. This, in turn could affect their populations.

Research is underway around the world, examining the conservation significance of such issues in more detail, but it’s another timely reminder of the profound ways in which we influence the environments we share with other species.

The authors  acknowledge Yvette Pauligk, who contributed to our published work at Mt Rothwell, and that the traditional custodians of this land are the Wathaurong people of the Kulin nation.
The Conversation

 

Identifying and prioritizing human behaviors that benefit biodiversity

Authors: Matthew J Selinske, Georgia E Garrard, Emily A Gregg, Alexander M Kusmanoff, Lindall R Kidd, Meghan T Cullen, Michelle Cooper, William L Geary, Melissa A Hatty, Fern Hames, Sarah Kneebone, Emily M McLeod, Euan G Ritchie, Zoe E Squires, Janelle Thomas, Madelaine A W Willcock, Sera Blair, and Sarah A Bekessy

Published in: Conservation Science and Practice

Abstract

The conservation profession is increasingly seeking effective ways to reduce societal impact on biodiversity, including through targeted behavior change interventions. Multiple conservation behavior change programs exist, but there is also great uncertainty regarding which behaviors are most strategic to target.

Behavioral prioritization is a tool that has been used effectively to support behavior change decision‐making in other environmental disciplines and more recently for a small sub‐set of biodiversity behavior change challenges.

Here, we use behavioral prioritization to identify individual behaviors that could be modified to achieve biodiversity benefits in the state of Victoria, Australia. We use an adapted nominal group technique method to identify potential biodiversity behaviors and, for each behavior, estimate the corresponding plasticity (or capacity for change) and positive impact on biodiversity outcomes.

We elicited 27 behaviors that individuals could undertake to benefit or reduce their negative impact on biodiversity. This list was then used to prioritize 10 behaviors as determined by their likely effect(s) on biodiversity, plasticity, and current prevalence in Victoria. We take a first step in outlining a list of behaviors that can direct Victorian decision‐makers toward increasing positive and reducing negative impacts of society on biodiversity, guide motivated individuals to reduce their own biodiversity footprint, and more broadly, develop a behavior change research agenda for behaviors most likely to benefit biodiversity.

Selinske MJ, Garrard GE, Gregg EA, Kusmanoff AM, Kidd LR, Cullen MT, Cooper M, Geary WL, Hatty MA, Hames F, Kneebone S, McLeod EM, Ritchie EG, Squires ZE, Thomas J, Willcock MAW, Blair S, Bekessy SA (2020) Identifying and prioritizing human behaviors that benefit biodiversity. Conservation Science and Practice PDF DOI

Evaluation of camera placement for detection of free-ranging carnivores; implications for assessing population changes

Authors: Hayley M Geyle, Michael Stevens, Ryan Duffy, Leanne Greenwood, Dale G Nimmo, Derek Sandow, Ben Thomas, John White, and Euan G Ritchie

Published in: Ecological Solutions and Evidence

Abstract

Introduced carnivores are often cryptic, making it difficult to quantify their presence in ecosystems, and assess how this varies in relation to management interventions. Survey design should thus seek to improve detectability and maximize statistical power to ensure sound inference regarding carnivore population trends. Roads may facilitate carnivore movements, possibly leading to high detectability. Therefore, targeting roads may improve inferences about carnivore populations.

We assessed our ability to monitor feral cats Felis catus and red foxes Vulpes vulpes on‐ and off‐road, with explicit consideration of the location of monitoring sites on our ability to detect population changes. We also assessed whether there was evidence of spatial or temporal interaction between these species that might influence their road‐use.

Surveys were conducted in a conservation reserve in south‐eastern Australia between 2016 and 2018. At each of 30 sites, we deployed two motion‐sensor cameras, one on‐road, and the other off‐road. Using occupancy models, we estimated cat and fox occupancy and detectability, and conducted a power analysis to assess our ability to detect declines in occupancy under three monitoring regimes (efforts targeted equally on‐ and off‐road, efforts targeted entirely off‐road and efforts targeted entirely on‐road).

On average, on‐road detectability was seven times higher for cats and three times higher for foxes. Targeting survey effort on‐road yielded the greatest power for detecting declines in both species, but our ability to detect smaller declines decreased with decreasing initial occupancy probability. No level of decline was detectable for cats when survey efforts were targeted off‐road, while only large declines (>50%) were detectable for foxes (assuming high initial occupancy probabilities). We found little evidence of spatial or temporal segregation, suggesting limited avoidance or suppression between the two species within this landscape.

Our results suggest that targeting monitoring on roads may be an effective approach for detecting declines in introduced carnivore populations, particularly following management intervention (e.g. lethal control), and in the face of resource limitations. We provide a framework that can help assist land managers to make informed decisions, which balance monitoring efforts and resource constraints with sufficient statistical power to assess management objectives.

Geyle HM, Stevens M, Duffy R, Greenwood L, Nimmo DG, Sandow D, Thomas B, White J, Ritchie EG (2020) Evaluation of camera placement for detection of free‐ranging carnivores; implications for assessing population changes. Ecological Solutions and Evidence PDF DOI

Run rabbit run: spotted-tailed quoll diet reveals invasive prey is top of the menu

Authors: Grant D Linley, Annette Rypalski, Georgeanna Story, and Euan G Ritchie

Published in: Australian Mammalogy

Abstract

Information about the ecological functional roles of native predators may help inform the conservation of wildlife and pest management.

If predators show preferences for certain prey, such as invasive species, this could potentially be used as a conservation tool to help restore degraded (e.g. overgrazed) ecosystems via the reintroduction of native predators and suppression of exotic prey (e.g. introduced herbivores).

The diet of spotted-tailed quolls was studied in a fenced reserve in south-eastern Australia where native mammals have been reintroduced, foxes and cats removed, but invasive European rabbits still persist.

A total of 80 scats were collected over 12 months and analysis of macroscopic prey remains was conducted to determine diet.

Rabbits were by far the most commonly consumed prey species by volume (~76%) and frequency (~60%), followed by brushtail possums (~11% for both volume and frequency), and other small and medium-sized native mammals in much smaller amounts. Quoll scat analysis revealed 10 mammal species in total, eight of which were native. Bird, reptile and invertebrate remains were uncommon in quoll scats.

This suggests that spotted-tailed quolls may show a preference for preying on invasive European rabbits in certain contexts, and this could potentially be used as part of quoll reintroductions to aid rabbit population suppression and ecosystem restoration.

Linley GD, Rypalski A, Story G, Ritchie EG (2020) Run rabbit run: spotted-tailed quoll diet reveals invasive prey is top of the menu. Australian Mammalogy PDF DOI

The Conversation: Cats wreak havoc on native wildlife, but we’ve found one adorable species outsmarting them

Long-nosed potoroo, Potorous tridactylus. Image credit: Zoos Victoria

 

By Euan Ritchie (Deakin University),Amy Coetsee (University of Melbourne),Anthony Rendall (Deakin University),Tim Doherty (University of Sydney), and Vivianna Miritis (University of Sydney).

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Feral and pet cats are responsible for a huge part of Australia’s shameful mammal extinction record. Small and medium-sized ground-dwelling mammals are most susceptible.

But we’ve found one mammal in particular that can outsmart cats and live alongside them: the long-nosed potoroo.

These miniature kangaroo-like marsupials are officially listed as vulnerable. And after the recent devastating fires, extensive swathes of their habitat in southeastern Australia were severely burnt, leaving them more exposed to predators such as foxes and cats. But the true extent of the impact on their numbers remains unclear.

Amid the devastation, our new study is reason to be optimistic.

Using motion-sensing camera traps on the wildlife haven of French Island – which is free of foxes, but not cats – we found potoroos may have developed strategies to avoid prowling cats, such as hiding in dense vegetation.

If these long-nosed potoroos can co-exist with one of the world’s most deadly predators, then it’s time we rethink our conservation strategies.

Surviving cats with a deadly game of hide and seek

We conservatively estimated that between five and 14 cats lived in our study area (but it takes only one cat to eradicate a population of native animals).

Although cats were common here, we detected them less often in areas of dense vegetation. By contrast, this was where we found potoroos more often.

Long-nosed potoroos are nocturnal foragers that mainly, but not exclusively, feed in more open habitat before sheltering in dense vegetation during the day. But we found potoroos rarely ventured out of their thick vegetation shelter.

This may be because they’re trading off potentially higher quality foraging habitat in more open areas against higher predation risk. In other words, it appears they’ve effectively learnt to hide from the cats.

Another intriguing result from our study was that although potoroos and feral cats shared more than half of their activity time, the times of peak activity for each species differed.

Cats were active earlier in the night, while potoroo activity peaked three to four hours later. This might be another potoroo strategy to avoid becoming a cat’s evening meal.

Still, completely avoiding cats isn’t possible. Our study site was in the national park on French Island, and it’s likely cats saturate this remnant patch of long-nosed potoroo habitat.

It’s also possible cats may be actively searching for potoroos as prey, and indeed some of our camera images showed cats carrying young long-nosed potoroos in their mouths. These potoroos were more likely killed by these cats, rather than scavenged.

Cats are expert hunters

Cats are exceedingly difficult to manage effectively. They’re adaptable, elusive and have a preference for live prey.

The two most common management practices for feral cats are lethal control and exclusion fencing. Lethal control needs to be intensive and conducted over large areas to benefit threatened species.

And outside of predator-free sanctuaries, it must be ongoing. If control stops, cats can reinvade from surrounding areas.

Safe havens” – created through the use of exclusion fencing or predator-free islands – can overcome some of these challenges. But while exclusion fencing is highly effective, it can create other bad outcomes, including an over-abundance of herbivores, leading to excessive grazing of vegetation.

Fencing and islands can result in native animals rapidly losing their anti-predator behaviour. This can limit the success of reintroducing them to areas outside predator-free havens.

In any case, removing introduced predators might not be really necessary in places native species can co-exist. If long-nosed potoroos have learnt to live with feral cats, we should instead focus on how to maintain their survival strategies.

Why cat eradication isn’t always the best option

It’s clear cats are here to stay, so we shouldn’t simply fall back largely on predator eradication or predator-free havens as the only way to ensure our wildlife have a fighting chance at long-term survival.

Yes, for some species, it’s vital to keep feral predators away. But for others like long-nosed potoroos, conserving and creating suitable habitat and different vegetation densities may be the best way to keep them alive.

But perhaps most important is having predator-savvy insurance populations, such as long-nosed potoroos on French Island. This is incredibly valuable for one day moving them to other areas where predators – native or feral – are present, such as nearby Phillip Island.

In the absence of predators, native wildlife can rapidly lose their ability to recognise predator danger. Programs aimed at eradicating introduced predators where they’re co-existing with native species need to pay careful attention to this.
The Conversation

Living with the enemy: a threatened prey species coexisting with feral cats on a fox-free island

Authors: Vivianna Miritis, Anthony R Rendall, Tim S Doherty, Amy L Coetsee, and Euan G Ritchie

Published in: Wildlife Research

Abstract

Context

Feral domestic cats (Felis catus) have contributed to substantial loss of Australian wildlife, particularly small- and medium-sized terrestrial mammals. However, mitigating cat impacts remains challenging.

Understanding the factors that facilitate coexistence between native prey and their alien predators could aid better pest management and conservation actions.

Aims

We estimated feral cat density, examined the impact of habitat cover on long-nosed potoroos (Potorous tridactylus tridactylus), and assessed the spatial and temporal interactions between cats and potoroos in the ‘Bluegums’ area of French Island, south-eastern Australia.

Materials and methods

We operated 31 camera stations across Bluegums for 99 consecutive nights in each of winter 2018 and summer 2018/19. We used a spatially explicit capture–recapture model to estimate cat density, and two-species single-season occupancy models to assess spatial co-occurrence of cats and potoroos.

We assessed the influence of vegetation cover and cat activity on potoroo activity by using a dynamic occupancy model. We also used image timestamps to describe and compare the temporal activities of the two species.

Key results

Bluegums had a density of 0.77 cats per km² across both seasons, although this is a conservative estimate because of the presence of unidentified cats.

Cats and long-nosed potoroos were detected at 94% and 77% of camera stations, respectively.

Long-nosed potoroo detectability was higher in denser vegetation and this pattern was stronger at sites with high cat activity.

Cats and potoroos overlapped in their temporal activity, but their peak activity times differed.

Conclusions

Feral cat density at Bluegums, French Island, is higher than has been reported for mainland Australian sites, but generally lower than in other islands.

Long-nosed potoroos were positively associated with cats, potentially indicating cats tracking potoroos as prey or other prey species that co-occur with potoroos.

Temporal activity of each species differed, and potoroos sought more complex habitat, highlighting possible mechanisms potoroos may use to reduce their predation risk when co-occurring with cats.

Implications

Our study highlighted how predator and prey spatial and temporal interactions, and habitat cover and complexity (ecological refuges), may influence the ability for native prey to coexist with invasive predators.

We encourage more consideration and investigation of these factors, with the aim of facilitating more native species to persist with invasive predators or be reintroduced outside of predator-free sanctuaries, exclosures and island safe havens.

Miritis V, Rendall AR, Doherty TS, Coetsee AL, Ritchie EG (2020) Living with the enemy: a threatened prey species coexisting with feral cats on a fox-free island. Wildlife Research PDF DOI

Moon phase and nocturnal activity of native Australian mammals

Authors: Grant D Linley, Yvette Pauligk, Courtney Marneweck, and Euan G Ritchie

Published in: Australian Mammology

Abstract

Moon phase and variation in ambient light conditions can influence predator and prey behaviour. Nocturnal predators locate prey visually, and prey may adjust their activity to minimise their predation risk. Understanding how native mammals in Australia respond to varying phases of the moon and cloud cover (light) enhances knowledge of factors affecting species’ survival and inference regarding ecological and population survey data.

Over a two-year period within a fenced conservation reserve, in south-eastern Australia, with reintroduced native marsupial predator and prey species (eastern barred bandicoot, southern brown bandicoot, long-nosed potoroo, rufous bettong, Tasmanian pademelon, brush-tailed rock-wallaby, red-necked wallaby, eastern quoll, spotted-tailed quoll, and naturally occurring swamp wallaby, common brushtail possum, common ringtail possum), we conducted monthly spotlight surveys during different moon phases (full, half and new moon).

We found an interaction between cloud cover and moon phase, and an interaction of the two depending on the mammal size and class. Increased activity of prey species corresponded with periods of increasing cloud cover. Predators and medium-sized herbivores were more active during times of low illumination.

Our findings suggest that moon phase affects the nocturnal activity of mammal species and that, for prey species, there might be trade-offs between predation risk and foraging. Our findings have implications for: ecological survey design and interpretation of results for mammal populations across moon phases, understanding predator and prey behaviour and interactions in natural and modified (artificial lighting) ecosystems, and potential nocturnal niche partitioning of species.

Linley GD, Pauligk Y, Marneweck C, Ritchie EG (2020) Moon phase and nocturnal activity of native Australian mammals. Australian Mammalogy PDF DOI

On the right track: placement of camera traps on roads improves detection of predators and shows non-target impacts of feral cat baiting

Authors: Michael L Wysong, Gwenllian D Iacona, Leonie E Valentine, Keith Morris, and Euan G Ritchie

Published in: Wildlife Research

Abstract

Context

To understand the ecological consequences of predator management, reliable and accurate methods are needed to survey and detect predators and the species with which they interact.

Recently, poison baits have been developed specifically for lethal and broad-scale control of feral cats in Australia. However, the potential non-target effects of these baits on other predators, including native apex predators (dingoes), and, in turn, cascading effects on lower trophic levels (large herbivores), are poorly understood.

Aims

We examined the effect that variation in camera trapping-survey design has on detecting dingoes, feral cats and macropodids, and how different habitat types affect species occurrences. We then examined how a feral cat poison baiting event influences the occupancy of these sympatric species.

Method

We deployed 80 remotely triggered camera traps over the 2,410-km² Matuwa Indigenous Protected Area, in the semiarid rangelands of Western Australia, and used single-season site-occupancy models to calculate detection probabilities and occupancy for our target species before and after baiting.

Key results

Cameras placed on roads were ~60 times more likely to detect dingoes and feral cats than were off-road cameras, whereas audio lures designed to attract feral cats had only a slight positive effect on detection for all target species.

Habitat was a significant factor affecting the occupancy of dingoes and macropodids, but not feral cats, with both species being positively associated with open woodlands.

Poison baiting to control feral cats did not significantly reduce their occupancy but did so for dingoes, whereas macropodid occupancy increased following baiting and reduced dingo occupancy.

Conclusions

Camera traps on roads greatly increase the detection probabilities for predators, whereas audio lures appear to add little or no value to increasing detection for any of the species we targeted.

Poison baiting of an invasive mesopredator appeared to negatively affect a non-target, native apex predator, and, in turn, may have resulted in increased activity of large herbivores.

Implications

Management and monitoring of predators must pay careful attention to survey design, and lethal control of invasive mesopredators should be approached cautiously so as to avoid potential unintended negative ecological consequences (apex-predator suppression and herbivore release).

Wysong ML, Iacona GD, Valentine LE, Morris K, Ritchie EG (2020) On the right track: placement of camera traps on roads improves detection of predators and shows non-target impacts of feral cat baiting. Wildlife Research PDF DOI

Space use and habitat selection of an invasive mesopredator and sympatric, native apex predator

Authors: Michael L Wysong, Bronwyn A Hradsky, Gwenllian D Iacona, Leonie E Valentine, Keith Morris, and Euan G Ritchie

Published in: Movement Ecology

Abstract

Background

Where mesopredators co-exist with dominant apex predators, an understanding of the factors that influence their habitat and space use can provide insights that help guide wildlife conservation and pest management actions.

A predator’s habitat use is defined by its home range, which is influenced by its selection or avoidance of habitat features and intra- and inter-specific interactions within the landscape. These are driven by both innate and learned behaviour, operating at different spatial scales.

We examined the seasonal home ranges and habitat selection of actively-managed populations of a native apex predator (dingo Canis dingo) and invasive mesopredator (feral cat Felis catus) in semi-arid Western Australia to better understanding their sympatric landscape use, potential interactions, and to help guide their management.

Methods

We used kernel density estimates to characterise the seasonal space use of dingoes and feral cats, investigate inter- and intra-species variation in their home range extent and composition, and examine second-order habitat selection for each predator. Further, we used discrete choice modelling and step selection functions to examine the difference in third-order habitat selection across several habitat features.

Results

The seasonal home ranges of dingoes were on average 19.5 times larger than feral cats. Feral cat seasonal home ranges typically included a larger proportion of grasslands than expected relative to availability in the study site, indicating second-order habitat selection for grasslands.

In their fine-scale movements (third-order habitat selection), both predators selected for roads, hydrological features (seasonal intermittent streams, seasonal lakes and wetlands), and high vegetation cover. Dingoes also selected strongly for open woodlands, whereas feral cats used open woodlands and grasslands in proportion to availability.

Management recommendations

Based on these results, and in order to avoid unintended negative ecological consequences (e.g. mesopredator release) that may stem from non-selective predator management, we recommend that feral cat control focuses on techniques such as trapping and shooting that are specific to feral cats in areas where they overlap with apex predators (dingoes), and more general techniques such as poison baiting where they are segregated.

Wysong ML, Hradsky BA, Iacona GD, Valentine LE, Morris K, Ritchie EG (2020) Space use and habitat selection of an invasive mesopredator and sympatric, native apex predator. Movement Ecology PDF DOI

Aussie English: Australia’s wildlife extinction crisis

In this podcast with Pete Smissen for Aussie English, I talk about a wide range of topics including:

  • how I became a wildlife ecologist
  • why large predators died out in Australia
  • how Australia’s past and present ecology differs
  • the impact of feral species in Australia including cats, foxes, and rabbits
  • why bushfires are so bad for Australia wildlife
  • the Australian wildlife extinction crisis
  • and more!

The Conversation: One little bandicoot can dig up an elephant’s worth of soil a year – and our ecosystem loves it

Eastern Barred Bandicoot, Perameles gunnii. Image credit Museum Victoria Catching The Eye via Flickr

By Euan Ritchie, (Deakin University), Amy Coetsee (University of Melbourne), Anthony Rendall  (Deakin University), Duncan Sutherland (University of Melbourne), and Leonie Valentine (University of Western Australia).

This article is republished from The Conversation under a Creative Commons license. Read the original article.

On Churchill Island, southeast of Melbourne, small cone-shaped, shallow holes (digs) puncture the grass. They’re widespread, and reveal moist soil below the surface. A soil heap at the entrance of a dig is a sign it was made recently.

Older digs are filled with leaves, grass, spiders, beetles and other invertebrates. They are made by hungry eastern barred bandicoots – small, roughly rabbit-sized digging marsupials – looking for a juicy worm or grub.

It turns out these bandicoot digs are far from just environmental curiosities – they can improve the properties and health of soils, and even reduce fire risk.

But eastern barred bandicoots are under threat from introduced predators like foxes and cats. In fact, they’re considered extinct in the wild on mainland Australia, so conservation biologists are releasing them on fox-free islands to help establish new populations and ensure the species is conserved long-term.

Our recent research on Churchill Island put a number on just how much the eastern barred bandicoot digs – and the results were staggering, showing how important they are for the ecosystem. But more on that later.

Why you should dig marsupial diggers

Digging mammals – such as bettongs, potoroos, bilbies and bandicoots – were once abundant and widespread across Australia, turning over large amounts of soil every night with their strong front legs as they dig for food or create burrows for shelter.

Their digs improve soil health, increase soil moisture and nutrient content, and decrease soil compaction and erosion. Digs also provide habitat for invertebrates and improve seed germination.

What’s more, by digging fuel loads (dry, flammable vegetation, such as leaves) into the soil, they can help bring down the risk of fire.

Rather than leaves and other plant matter accumulating on the soil surface and drying out, this material is turned over faster, entering the soil when the badicoots dig, which speeds up its decay. Research from 2016 showed there’s less plant material covering the soil surface when digging mammals are about. Without diggers, models show fire spread and flame height are bigger.

In fact, all their functions are so important ecologists have dubbed these mighty diggers “ecosystem engineers”.

Losing diggers leads to poorer soil health

Of Australia’s 29 digging mammals, 23 are between 100 grams and 5 kilograms. Most are at risk of cat and fox predation, and many of these are officially listed as threatened species by the International Union for Conservation of Nature.

Since European settlement, six of Australia’s digging mammals have gone extinct, including the lesser bilby, desert rat kangaroo and pig-footed bandicoots. Many others have suffered marked population declines and extensive range contraction through habitat destruction and the introduction of foxes and cats.

Tragically, the widespread decline and extinction of many digging mammals means soil and ecosystem health has suffered as well.

Soils that were once soft textured, easy to crumble, rich and fertile are now often compact, repel water and nutrient poor, impeding seed germination and plant growth. Fuel loads are also likely to be much higher now than in the past, as less organic matter is dug into the soil.

To date, most research on digging mammals has focused on arid environments, with much less known about how digging influences wetter (mesic) environments. But our recently published study on eastern barred bandicoots provides new insights.

Just how much do bandicoots dig anyway?

In 2015, 20 mainland eastern barred bandicoots were released onto Churchill Island in Victoria’s Westernport Bay.

On mainland Australia, fox predation has driven this species to near extinction, and it’s classified as extinct in the wild. All Victoria’s islands are beyond the historic range of eastern barred bandicoots, but fox-free islands could be how we recover them.

Introducing bandicoots on Churchill Island presented the perfect opportunity to quantify how they influence soil properties when digging for food.

To do this we recorded the number of digs bandicoots made each night and measured the volume of soil they displaced through digging. We also compared soil moisture and compaction within the digs, versus un-dug soil – and we didn’t expect what we found.

In one night on Churchill Island, one bandicoot can make 41 digs an hour. That’s nearly 500 digs a night, equating to around 13 kilograms of soil being turned over every night, or 4.8 tonnes a year. That’s almost as much as the average weight of a male African elephant.

So, an astonishing amount of soil is being turned over, especially considering these bandicoots typically weigh around 750 grams.

If you multiply this by the number of bandicoots on Churchill Island (up from 20 in 2015 to around 130 at the time of our study in 2017), there’s a staggering 1,690 kilos of soil being dug up every night. That’s some major earthworks!

However, we should note our study was conducted during the wetter months, when soils are typically easier to dig.

In summer, as soil becomes harder and drier on Churchill Island, digging may become more difficult. And bandicoots, being great generalists, feed more on surface invertebrates like beetles and crickets, resulting in fewer digs. So we expect in summer that soil is less disturbed.

Bandicoots might help agriculture too

All this digging was found to boost soil health on Churchill Island. This means eastern barred bandicoots may not only play an important role in ecosystem health and regeneration, but also potentially in agriculture by assisting pasture growth and condition, reducing topsoil runoff, and mitigating the effects of trampling and soil compaction from livestock.

The benefits bandicoot digs have across agricultural land is of particular importance now that eastern barred bandicoots have also been released on Phillip Island and French Island, and are expected to extensively use pasture for foraging.

These island releases could not just help to ensure eastern barred bandicoots avoid extinction, but also promote productive agricultural land for farmers.

So, given the important ecological roles ecosystem engineers like bandicoots perform, it’s also important we try to reestablish their wild populations on the mainland and outside of fenced sanctuaries so we can all benefit from their digging, not just on islands.
The Conversation

The Conversation: How you can help – not harm – wild animals recovering from bushfires

Building one of these watering pods can help thirsty wildlife, but it must be checked for safety and hygiene, and refilled regularly. Image credits: Arid Recovery

By Marissa Parrott (University of Melbourne), Dale Nimmo (Charles Sturt University) and Euan Ritchie (Deakin University).

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Since July last year, bushfires have burned more than 7.7 million hectares of southeast Australia, putting many threatened species at increased risk of extinction.

Now that fires have been extinguished in some areas, surviving wildlife face other challenges, such as a lack of food, clean water and shelter, and more exposure to invasive predators.

Australians have helped raise millions of dollars to support Australia’s imperilled wildlife, such as to set up triage centres and evacuate threatened species like eastern bristlebirds and Macquarie perch.

But beyond the vital role of providing financial support, here are a few simple things individuals can do – and avoid – to help our native wildlife recover.

Animals need fresh water, but not from a bottle

Photos of well-meaning people offering water from bottles to animals, especially thirsty koalas, often go viral online. But this is not a safe way to help koalas.

Animals must be allowed to drink water themselves, rather than us pouring water into their mouths. Animals, such as koalas, can’t drink quickly and poured water can fill their lungs, leading to potentially fatal aspiration pneumonia.

Still, providing safe, fresh drinking water is one crucial and practical way we can help them as summer grinds on.

This is particularly important since recent storms have washed ash, sediment and chemicals from burnt infrastructure into waterways, contaminating many catchments.

Water should be stationed at ground level, in a shaded location safe from predators, and in trees for birds and tree-dwelling species like possums, gliders and koalas. Check out DIY guides for building drinking fountains, or “watering pods”, for wildlife.

Sticks and rocks should be placed in the water to allow small species, such as reptiles, to climb out if they fall in. Water must be checked and changed regularly to ensure hygiene and avoid the spread of disease. And pets must be kept away from these locations (especially cats).

What to do if you spot injured wildlife by the road

Authorities are searching the fire grounds for injured animals, and the public is reminded to avoid these areas until they’re confirmed as safe to enter.

But if you happen upon an injured survivor, what should you do?

First of all, call government agencies or trained wildlife rescuers, who can assist any injured wildlife.

Many animals may be in pain and frightened and some, including kangaroos, koalas and wombats, are potentially dangerous if approached. In urgent cases, such as when an animal is in obvious distress or has clear injuries, some animals can be carefully caught and wrapped in a towel, then placed in a well-ventilated, dark and secure box for quiet transport to wildlife veterinary hospitals for care.

Sadly, many animals are hit by cars during fires when they’re disoriented and panicked, and so it’s important to slow down in such areas.

You can also check animals found by roads for injuries and surviving young in pouches, and call authorities to assist. But always be careful of traffic when attending to animals on roadsides, and help other drivers be aware of you by putting hazard lights on and wearing bright clothes.

Don’t feed native wildlife, especially not peanut butter mixes

With so much vegetation burned away, supplementary feeding has gained attention following fires in New South Wales, Victoria and South Australia.

But feeding wildlife without expert advice and legal approval can do more harm than good.

Feeding inappropriate foods like processed foods, over-feeding, providing unhygienic foods or food stations, and attracting predators to food stations, can all be fatal for native wildlife.

Even some foods suggested online, such as bait balls (peanut butter mixes), can cause gastrointestinal issues for wildlife, potentially killing them. Similar issues can arise if wildlife are given some types of hay, vegetables, seeds, and fruits.

Supplementary feeding isn’t advised unless habitat and sources of food have been completely destroyed, and is only appropriate as a short-term emergency intervention until natural resources recover.

But leave it up to the experts and government agencies, which provide nutritionally suitable, specially developed and monitored food in extreme cases.

Somewhere to run and hide

In some cases, fire may mean native animals are more prone to predators killing and eating them. And, depending on the habitat, it may take months or even years for plants and animals’ homes to recover sufficiently to provide safety once again.

However, new approaches – such as building artificial shelters out of fencing wire and shade cloth – may help to buy species time, keeping small mammals, reptiles and other potential prey safe from hungry mouths. This could occur both on private and public land.

Show wildlife the money

Caring for wildlife after fires, whether they’re injured or have lost their homes, is a marathon, not a sprint. And given the scale of these fires, our wild neighbours need our increased support.

Often, the most helpful thing people can do is raise and donate funds to organisations, including Zoos Victoria and the Ecological Society of Australia.

Some wildife species, such as bristlebirds, corroboree frogs, and mountain pygmy-possums, are being pushed to the brink of extinction and may need long-term captive breeding and release programs, or investment in active management of wild populations (such as the newly constructed feral predator-free area for Kangaroo Island dunnarts).

We can all help to make a difference and protect our remarkable and unique wildlife that so desperately needs our help.The Conversation

After the catastrophe: a blueprint for a conservation response to large-scale ecological disaster

Authors: Chris Dickman, Don Driscoll, Stephen Garnett, David Keith, Sarah Legge, David Lindenmayer, Martine Maron, April Reside, Euan Ritchie, James Watson, Brendan Wintle, and John Woinarski

The wildfires that afflicted Australia in the summer of 2019-2020 was ecological disaster at enormous scale, and without comparable precedent. With escalating global climate change, such large-scale ecological catastrophes are likely to become more widespread and frequent. Here, we describe a blueprint for conservation responses to these wildfires, to document the challenge and attempted solutions to this particular event and as a potential template for dealing with comparable future events.

The purpose of this report, published as part of the Threatened Species Recovery Hub, is to frame a comprehensive set of linked responses to large-scale impacts for conservation across immediate to longer time frames, in order to best achieve the recovery of affected species, ecosystems and ecological health.

Dickman C, Driscoll D, Garnett S, Keith D, Legge S, Lindenmayer D, Maron M, Reside A, Ritchie EG, Watson J, Wintle B, Woinarski J (2020) After the catastrophe: a blueprint for a conservation response to large-scale ecological disaster. Threatened Species Recovery Hub PDF LINK

The Conversation: Hunter, hunted: when the world catches on fire, how do predators respond?

Some predators, including red foxes, move into burnt areas after fires pass through. Image credit: Alexandre Roux via Flickr

By Euan Ritchie (Deakin University), Ayesha Tulloch (University of Sydney), Dale Nimmo (Charles Sturt University), Tim Doherty (Deakin University) and William Geary (Deakin University).

This article is republished from The Conversation under a Creative Commons license. Read the original article.

2019 might well be remembered as the year the world caught fire. Some 2.9 million hectares of eastern Australia have been incinerated in the past few months, an area roughly the same size as Belgium. Fires in the Amazon, the Arctic, and California captured global attention.

As climate change continues, large, intense, and severe fires will become more common. But what does this mean for the animals living in fire-prone environments?

Our new research, published recently in the Journal of Animal Ecology, looked at studies from around the world to identify how predators respond to fire.

We found some species seem to benefit from fires, others appear to be vulnerable, and some seem indifferent. In a changing climate, it’s urgent we understand how fires affect predators – and hence potentially their prey –in order to keep ecosystems healthy.

Predators: the good and the bad

Large predators, like wolves and lions, often play important roles in ecosystems, regulating food webs by reducing the numbers or changing the behaviour of herbivores and smaller predators. Many large predators are in dire straits within their native range, while introduced predators, such as feral cats and red foxes, have spread to new regions, where they have devastated native wildlife .

Fires can offer new opportunities as well as problems to predators. Some predators take advantage of charred, more open landscapes to hunt vulnerable prey; others rely on thick vegetation to launch an ambush.

But until now, we have not known which predators are drawn to fire, which are repelled by it, and which don’t care either way. Synthesising information on how different kinds of predators (for example, large or small, pursuit or ambush) respond to fire is vital for both the conservation of top predators and to help protect native prey from introduced predators.

Some like it hot

Our research reviewed studies from around the world to identify how different vertebrate predators (birds, mammals and reptiles) respond to fire in different ecosystems.

We found 160 studies on the response of 188 predator species to fire, including wolves, coyotes, foxes, cats, hawks, owls, goannas and snakes, amongst others. The studies came from 20 different countries, although most were from North America or Australia, and focused on canine and feline species.

Some predators seem to like fire: they are more abundant, or spend more time in, recently burnt areas than areas that escape fire. Our review found red foxes (Vulpes vulpes) mostly responded positively to fire and become more active in burned areas.

Raptors have even been observed in Northern Australia carrying burning sticks, helping to spread fire and targeting prey as they flee the fire.

For other predators, fire is bad news. Following Californian wildfires, numbers of eastern racer snakes fell in burnt areas. Likewise, lions avoid recently burned areas, because they rely on dense vegetation from which to ambush prey.

The authors of the papers we reviewed thought food availability, vegetation cover, and competition with other predators were the most important things affecting species’ responses to fire.

But perhaps more surprising was that most species, including bobcats and the striped skunk, appeared largely unaffected by fire. Of the affected species, some (such as spotted owls) responded differently to fire in different places.

Overall, we found it is difficult to predict how a predator species will respond to fire.

We still have a lot to learn

Our results show while many predators appear to adapt to the changes that fires bring about, some species are impacted by fire, both negatively and positively. The problem is that, with a few exceptions, we will struggle to know how a given fire will affect a predator species without local knowledge. This means environmental managers need to monitor the local outcomes of fire management, such as fuel reduction burns.

There may be situations in which predator management needs to be coupled with fire management to help prevent native wildlife becoming fox food after fire. There has even been trials to see if artificial shelters can help protect native wildlife from introduced predators after fire.

Getting our knowledge base right

One thing that has hampered our research is the lack of contextual information in many studies. No two fires are the same – they differ in size, intensity, severity, and season – but these details are often absent. The literature is also biased towards dog-like and cat species, and there are few studies on the response of predators to fire in Africa, Asia, and South America.

It is important to note that some predator responses to fire may be overlooked due to the way experiments were carried out, or because monitoring happened too long after the fire.

Unifying how fire, predator numbers and environmental features are recorded would help future studies predict how predators might react to different types of fires in various situations.

As wildfires become more frequent and severe under climate change, understanding how fire intensity and frequency shapes predator populations and their prey will be critical for effective and informed ecosystem management and conservation.
The Conversation

The Conversation: Double trouble as feral horse numbers gallop past 25,000 in the Australian Alps

Feral horses are a growing problem for the NSW government. Image credit: Constantin Stanciu via Shutterstock

By Don Driscoll (Deakin University), David M Watson (Charles Sturt University), and Euan Ritchie (Deakin University).

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Feral horse numbers have more than doubled in the past five years in the Australian Alps, according to results just released from the Australian Alps Feral Horse Aerial Survey. In one of the three survey blocks, North Kosciuszko, feral horse numbers have risen from an estimated 3,255 in 2014 to 15,687 in 2019, a near five-fold increase.

Scientists warned the government that very high numbers of horses would be the inevitable consequence of its inaction over horse management.

With no horses removed in 2017 or 2018, and only 99 removed this year, the population has been allowed to grow at about 23% per year, close to the maximum of about 25% known for feral horses.

More than just allowing numbers to increase, the NSW parliament legislated to protect feral horses within Kosciuszko National Park, effectively prioritising the preservation of horse populations over native alpine species and environmental values, where they are in conflict.

This was despite the strong advice from scientists, and amid substantial controversy around the origins and timing of the bill.

A potentially fatal feral horse problem

High feral horse numbers forced the closure of the popular Blue Waterholes campground in November, after substantial risks and several injuries to visitors were reported. Freedom of information requests were needed to bring to light crashes between cars and feral horses in Kosciuszko.

Despite the NSW government trying to keep this information from reaching the public, several incidents of feral horses being struck by vehicles have now been reported.

The community group Reclaim Kosci has warned it is only a matter of time before someone is killed in a collision with a feral horse unless numbers are drastically and rapidly reduced.

Besides impacts on people, the lack of effective feral horse policy in NSW has now set the stage for another mass animal welfare disaster.

With an estimated 25,318 feral horses distributed across the surveyed area (more than 7,400 square kilometres) of the Australian Alps, many thousands of horses will face starvation when the region next burns. This is predictable, inevitable and tragically also completely avoidable had effective feral horse control been implemented.

The prolonged drought hitting Australia has worsened the impacts of horses in the high country. Plants already struggling to survive are being trampled and grazed, and areas around standing water resemble feedlots.

These impacts will worsen over summer, both for the national park and the horses themselves, with herds suffering in the heat and struggling to survive. Horses starved to death along the snowy river in Kosciuszko in 2018.

Now many more animals are at risk of this fate because scientifically-supported solutions have been dismissed by NSW deputy premier John Barilaro.

Natural wildlife threatened

Evidence presented at the Kosciuszko Science Conference and research published earlier this year showed how a broad range of Alpine species and ecosystems were being affected by feral horses. These effects will now be more intense and occur across more of Australia’s ecologically sensitive and biodiverse alpine environments.

For example, the native broad toothed rat depends on dense vegetation along watercourses. With feral horses eating out or trampling plants along streams, these delightful, rotund fur-balls may lose their homes, and hence be more exposed to the elements and predators.

Right now, feral horses are reducing the habitat for these animals, causing already threatened populations to become smaller and more fragmented. As these small populations blink into extinction we can expect widespread losses across the national park.

Corroboree frogs will now be under enormous pressure. We already know feral horses destroy the wetlands these iconic yellow-striped black frogs depend on for breeding. This destruction will likely now impact many more swamps, reducing breeding success and reducing options for reintroduction of this critically endangered frog.

Another species, the Stocky Galaxias, teeters on the brink of extinction. This small native fish now only lives in a 3km stretch of stream in Kosciuszko National Park. Feral horses trample the river banks and rip out vegetation that causes silt to accumulate in the stream.

This is disastrous for the fish, which breed beneath boulders in the stream. If silt fills up the gaps beneath boulders, there is no place for the fish to lay eggs.

The high numbers of feral horses in Kosciuszko mean this process of stream destruction will likely worsen, potentially hastening the demise of this species unique to Kosciuszko National Park.

New management plan needed

Hope for change now rests with the new feral horse management plan being developed by the recently established Kosciuszko National Park Wild Horse Community Advisory Panel and the Wild Horse Scientific Advisory Panel. The community panel has expressed interest in working with the scientific panel, and such collaboration will be essential for making progress.

These committees will need to consider all options for resolving this human safety, animal welfare, and ecological crisis. Although trapping is crueller and many times more expensive than aerial culling, if the trapping effort is substantially ramped up across the park, it could potentially limit population growth and reduce horse numbers.

Aerial culling, despite being the most cost-effective and humane method to lower the horse population size and reduce impacts, is misrepresented by the pro-brumby lobby and sections of the media as cruel, and hence has been deemed unacceptable. These costs, and animal welfare and political trade-offs, must be carefully considered by the committees.

The scientific committee said the draft plan for action will be open for comment in February 2020 to meet NSW environment minister Matt Kean’s deadline for a final plan by May 1, 2020. This rapid timeframe is absolutely essential, as the increase of feral horses in the Alpine National Park will not abate any time soon without urgent and substantial control measures.
The Conversation

Predator responses to fire: A global systematic review and meta‐analysis

Authors: William L Geary, Tim S Doherty, Dale G Nimmo, Ayesha I T Tulloch, and Euan G Ritchie

Published in: Journal of Animal Ecology

Abstract

Knowledge of how disturbances such as fire shape habitat structure and composition, and affect animal interactions, is fundamental to ecology and ecosystem management. Predators also exert strong effects on ecological communities, through top‐down regulation of prey and competitors, which can result in trophic cascades. Despite their ubiquity, ecological importance and potential to interact with fire, our general understanding of how predators respond to fire remains poor, hampering ecosystem management.

To address this important knowledge gap, we conducted a systematic review and meta‐analysis of the effects of fire on terrestrial, vertebrate predators worldwide. We found 160 studies spanning 1978–2018. There were 36 studies with sufficient information for meta‐analysis, from which we extracted 96 effect sizes (Hedge’s g) for 67 predator species relating to changes in abundance indices, occupancy or resource selection in burned and unburned areas, or before and after fire.

Studies spanned geographic locations, taxonomic families, and study designs, but most were located in North America and Oceania (59% and 24%, respectively), and largely focussed on felids (24%) and canids (25%). Half (50%) of the studies reported responses to wildfire, and nearly one third concerned prescribed (management) fires.

There were no clear, general responses of predators to fire, nor relationships with geographic area, biome or life history traits (e.g. body mass, hunting strategy and diet). Responses varied considerably between species. Analysis of species for which at least three effect sizes had been reported in the literature revealed that red foxes (Vulpes vulpes) mostly responded positively to fire (e.g. higher abundance in burned compared to unburned areas) and eastern racers (Coluber constrictor) negatively, with variances overlapping zero only slightly for both species.

Our systematic review and meta‐analysis revealed strong variation in predator responses to fire, and major geographic and taxonomic knowledge gaps. Varied responses of predator species to fire likely depend on ecosystem context. Consistent reporting of ongoing monitoring and management experiments is required to improve understanding of the mechanisms driving predator responses to fire, and any broader effects (e.g. trophic interactions). The divergent responses of species in our study suggest that adaptive, context‐specific management of predator‐fire relationships is required.

Geary WL, Doherty TS, Nimmo DG, Tulloch AIT, Ritchie EG (2019) Predator responses to fire: A global systematic review and meta‐analysis. Journal of Animal Ecology PDF DOI 

Digging up the dirt: quantifying the effects on soil of a translocated ecosystem engineer

Authors: Lauren M Halstead, Duncan R Sutherland, Leonie E Valentine, Anthony R Rendall, Amy L Coetsee, and Euan G Ritchie

Published in: Austral Ecology

Abstract

Digging mammals are often considered ecosystem engineers, as they affect important properties of soils and in turn nutrient exchange, vegetation dynamics and habitat quality. Returning such species, and their functions, to areas from where they have been extirpated could help restore degraded landscapes and is increasingly being trialled as a conservation tool.

Studies examining the effects of digging mammals have largely been from arid and semi‐arid environments, with little known about their impacts and importance in mesic systems. To address this knowledge gap, we investigated the ecological role of a recently introduced population of eastern barred bandicoots (Perameles gunnii) on Churchill Island, Victoria, south‐eastern Australia, from which all digging mammals have been lost.

We quantified the annual rate of soil turnover by estimating the number of foraging pits bandicoots created in 100‐m² plots over a 24‐hour period. Foraging pit counts could not be completed in each season, and the overall turnover estimate assumes that autumn/winter months represent turnover rates for the entire year; however, this is likely to fluctuate between seasons. Ten fresh and ten old pits were compared to paired undug control sites to quantify the effect soil disturbance had on soil hydrophobicity, moisture content and soil strength. Plots contained between zero and 64 new foraging pits each day. We estimated that an individual eastern barred bandicoot digs ~487 (95% CI = 416–526) small foraging pits per night, displacing ~13.15 kg (95% CI = 11.2–14.2 kg) of soil, equating to ~400 kg (95% CI = 341–431 kg) of soil in a winter month. Foraging pits were associated with decreased soil compaction and increased soil moisture along the foraging pit profile.

Eastern barred bandicoots likely play an important role in ecosystems through their effects on soil, which adds to an increasing body of knowledge suggesting restoration of ecosystems, via the return of ecosystem engineers and their functions, holds much promise for conserving biodiversity and ecological function.

Halstead LM, Sutherland DR, Valentine LE, Rendall AR, Coetsee AL, Ritchie EG (2019) Digging up the dirt: Quantifying the effects on soil of a translocated ecosystem engineer. Austral Ecology PDF DOI

Constraints on vertebrate range size predict extinction risk

Authors: Thomas M Newsome, Christopher Wolf, Dale G Nimmo, R Keller Kopf, Euan G Ritchie, Felisa A Smith, and William J Ripple

Published in: Global Ecology and Biogeography

Abstract

Aim: The only factor in the fossil record that consistently buffers against extinction risk is large geographical range. We ask whether extant vertebrate species with the smallest geographical range for their body size have a higher extinction risk, and thus whether the lower bound of the modern range–body size relationship could serve as an effective conservation prioritization tool.

Location: Global in scope.

Time period: Modern.

Major taxa studied: Six classes of vertebrates.

Methods: We compiled a database of geographical range, body size and extinction risk for six vertebrate classes (n = 26,076). We characterized the shape of the relationship between geographical range and body size for each class, using 90% and 10% quantile regression to describe the upper and lower bounds, respectively. We then evaluated the degree of extinction vulnerability of species at the lower bound of the regression using generalized linear mixed models. All analyses accounted for phylogenetic dependence between related species.

Results: The relationships between species ranges and body sizes were generally positive at both the upper and the lower bounds, and segmented (nonlinear) relationships were common. Despite this variability, species near the lower boundary of the relationship were more often in higher extinction risk categories, and this remained true when the role of range size in the International Union for Conservation of Nature Red Listing criteria was accounted for.

Main conclusions: Variability in the upper and lower bounds of the range–body size relationship suggests that some classes of vertebrates exhibit combinations of ranges and body sizes that might not reflect historical patterns. Nonetheless, the range–body size relationship remains a reliable and useful predictor of extinction risk, more so than range size does alone. The range–body size relationship could therefore be used to track the trajectories of species towards or away from an extinction threshold and allow the tracking of how different human activities alter the range–body size relationship.

Newsome TM, Wolf C, Nimmo DG, Kopf RK, Ritchie EG, Smith FA, Ripple WJ (2019) Constraints on vertebrate range size predict extinction risk, Global Ecology and Biogeography PDF DOI