There is growing recognition of the important roles played by predators in regulating ecosystems and sustaining biodiversity. Much attention has focused on the consequences of predator-regulation of herbivore populations, and associated trophic cascades. However apex predators may also control smaller 'mesopredators' through intraguild interactions. Removal of apex predators can result in changes to intraguild interactions and outbreaks of mesopredators ('mesopredator release'), leading in turn to increased predation on smaller prey. Here we provide a review and synthesis of studies of predator interactions, mesopredator release and their impacts on biodiversity. Mesopredator suppression by apex predators is widespread geographically and taxonomically. Apex predators suppress mesopredators both by killing them, or instilling fear, which motivates changes in behaviour and habitat use that limit mesopredator distribution and abundance. Changes in the abundance of apex predators may have disproportionate (up to fourfold) effects on mesopredator abundance. Outcomes of interactions between predators may however vary with resource availability, habitat complexity and the complexity of predator communities. There is potential for the restoration of apex predators to have benefits for biodiversity conservation through moderation of the impacts of mesopredators on their prey, but this requires a whole-ecosystem view to avoid unforeseen negative effects. 'Nothing has changed since I began. My eye has permitted no change. I am going to keep things like this.' From 'Hawk Roosting', by Ted Hughes.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2009.01347.x

Predator interactions, mesopredator release and biodiversity conservation

Invasive species threaten biodiversity globally, and invasive mammalian predators are particularly damaging, having contributed to considerable species decline and extinction. We provide a global metaanalysis of these impacts and reveal their full extent. Invasive predators are implicated in 87 bird, 45 mammal, and 10 reptile species extinctions—58% of these groups’ contemporary extinctions worldwide. These figures are likely underestimated because 23 critically endangered species that we assessed are classed as “possibly extinct.” Invasive mammalian predators endanger a further 596 species at risk of extinction, with cats, rodents, dogs, and pigs threatening the most species overall. Species most at risk from predators have high evolutionary distinctiveness and inhabit insular environments. Invasive mammalian predators are therefore important drivers of irreversible loss of phylogenetic diversity worldwide. That most impacted species are insular indicates that management of invasive predators on islands should be a global conservation priority. Understanding and mitigating the impact of invasive mammalian predators is essential for reducing the rate of global biodiversity loss.

https://www.pnas.org/content/pnas/113/40/11261.full.pdf

Invasive predators and global biodiversity loss

Technological advances have enabled a new class of multivariate models for ecology, with the potential now to specify a statistical model for abundances jointly across many taxa, to simultaneously explore interactions across taxa and the response of abundance to environmental variables. Joint models can be used for several purposes of interest to ecologists, including estimating patterns of residual correlation across taxa, ordination, multivariate inference about environmental effects and environment-by-trait interactions, accounting for missing predictors, and improving predictions in situations where one can leverage knowledge of some species to predict others. We demonstrate this by example and discuss recent computation tools and future directions.

So Many Variables: Joint Modeling in Community Ecology.

1. Introduction 2. Critiques of statistical methods 3. Analysing averages and frequencies 4. How good are the models? 5. Regression and correlation 6. Analysis of variance Case studies 7. Mark-recapture analysis 8. Effects of marking frogs 9. Population dynamics 10. Subjective priors 11. Conclusion Appendix A. A tutorial for running WinBUGS Appendix B. Probability distributions Appendix C. MCMC algorithms.

/pdf/bayesian-methods-for-ecology-3tg8hj8e6u.pdf

Bayesian Methods for Ecology

6 Climatic changes associated with the El Nino Southern Oscillation (ENSO) can have a dramatic impact on ter- restrial ecosystems worldwide, but especially on arid and semiarid systems, where productivity is strongly lim- ited by precipitation. Nearly two decades of research, including both short-term experiments and long-term studies conducted on three continents, reveal that the initial, extraordinary increases in primary productivity percolate up through entire food webs, attenuating the relative importance of top-down control by predators, providing key resources that are stored to fuel future production, and altering disturbance regimes for months or years after ENSO conditions have passed. Moreover, the ecological changes associated with ENSO events have important implications for agroecosystems, ecosystem restoration, wildlife conservation, and the spread of disease. Here we present the main ideas and results of a recent symposium on the effects of ENSO in dry ecosystems, which was convened as part of the First Alexander von Humboldt International Conference on the El Nino Phenomenon and its Global Impact (Guayaquil, Ecuador, 16-20 May 2005).

/pdf/extreme-climatic-events-shape-arid-and-semiarid-ecosystems-5e0y2l62tq.pdf

Extreme climatic events shape arid and semiarid ecosystems

Populations of rodents were studied for periods of 7−9 years at each of three sites in arid Australia. All species fluctuated dramatically in abundance, being absent or in low numbers during droughts but erupting after significant rainfall. Strong correlations were obtained between capture rates and cumulative monthly rainfall residuals, with time lags, that had been modified by an exponential decay function to model the post-rain depletion of resources. The introduced Mus domesticus erupted within only two months of exceptional rainfall at one site, whereas the native rodents Notomys alexis, Pseudomys hermannsburgensis and P. desertor generally responded 3Œ10 months after rain. The faster response of M. domesticus reflects its high reproductive potential compared with the native rodents, and perhaps greater immigration. Differences in magnitudes and delays in response to rainfall among the native species were due probably to differences in initial population sizes and times available for response and, for P. desertor, to between-site differences in the quality or quantity of food resources. Population declines in all species during dry periods probably followed resource shortages. Despite the usually strong linkage between rainfall and population dynamics, rain failed to trigger population responses in rodents for prolonged periods at two of the sites, and was not clearly associated with an eruption of P. hermannsburgensis at the third. The lack of a population response at one site was attributed to predation, but events at the other two remain unexplained. We conclude that long-term studies should play an important role in describing temporal changes in rodent populations in arid Australia and, with field experiments, in evaluating how rainfall and other factors combine to effect the changes.

/pdf/long-term-dynamics-of-rodent-populations-in-arid-australia-b0ducqbe5p.pdf

Long-term dynamics of rodent populations in arid Australia: the influence of rainfall

Aim
Reducing the impacts of feral cats (Felis catus) is a priority for conservation managers across the globe, and success in achieving this aim requires a detailed understanding of the species’ ecology across a broad spectrum of climatic and environmental conditions. We reviewed the diet of the feral cat across Australia and on Australian territorial islands, seeking to identify biogeographical patterns in dietary composition and diversity, and use the results to consider how feral cats may best be managed.

Location
Australia and its territorial islands.

Methods
Using 49 published and unpublished data sets, we modelled trophic diversity and the consumption of eight food groups against latitude, longitude, mean temperature, precipitation, environmental productivity and climate-habitat regions.

Results
We recorded 400 vertebrate species that feral cats feed on or kill in Australia, including 28 IUCN Red List species. We found evidence of continental-scale prey-switching from rabbits to small mammals, previously recorded only at the local scale. The consumption of arthropods, reptiles, rabbits, rodents and medium-sized native mammals varied with different combinations of latitude, longitude, mean annual precipitation, temperature and environmental productivity. The frequency of rodents and dasyurids in cats’ diets increased as rabbit consumption decreased.

Main conclusions
The feral cat is an opportunistic, generalist carnivore that consumes a diverse suite of vertebrate prey across Australia. It uses a facultative feeding strategy, feeding mainly on rabbits when they are available, but switching to other food groups when they are not. Control programmes aimed at culling rabbits could potentially decrease the availability of a preferred food source for cats and then lead to greater predation pressure on native mammals. The interplay between cat diet and prey species diversity at a continental scale is complex, and thus cat management is likely to be necessary and most effective at the local landscape level.

A continental‐scale analysis of feral cat diet in Australia

Fire-driven succession and a period of high rainfall had a pronounced effect on the distribution and abundance of small mammals inhabiting spinifex grassland in Uluzu National Park from 1987 to 1990. Species richness and abundance were generally higher on sites burnt in 1976, where six species (Pseudomys hermannsburgensis, Pseudomys desertor, Mus domesticus, Dasycercus cristicauda, Ningaui ridei and Sminthopsis youngsoni) were caught more frequently. Two species (Notomys alexis and Sminthopsis hirtipes) were more abundant on sites burnt in 1986. Murid rodent numbers fluctuated substantially following high rainfall. The number of individuals increased 100-fold, and species richness increased from two to four when P. desertor and M. domesticus appeared in the second year of the study. In contrast, captures of dasyurid marsupials increased only slightly over the three years, with the most dramatic increase occurring for D. cristicauda. This study highlights the importance of fire as a management tool. Patch burning within spinifex grasslands maximises species diversity of small mammals by ensuring that suitable successional states are present at all times. This is particularly important for species that are restricted in their distribution, such as D. cristicauda

The effects of fire-driven succession and rainfall on small mammals, in Spinifex grassland at Uluru National Park, Northern Territory

Context The ability to monitor changes in population abundance is critical to the success of pest animal management and research programs. Feral cats (Felis catus) are an important pest animal, but current monitoring techniques have limited sensitivity or are limited in use to particular circumstances or habitats. Recent advances in camera-trapping methods provide the potential to identify individual feral cats, and to use this information to estimate population abundances using capture–mark–recapture (CMR) methods. Aims Here, we use a manipulative study to test whether camera-trapping and CMR methods can be used to estimate feral cat abundances. Methods We established a grid of infrared cameras and lure stations over three pastoral properties on Kangaroo Island, Australia, for 15 days. We then reduced the population abundance with an intensive trapping program and repeated the camera survey. We estimated population abundances using robust design CMR models, and converted abundance estimates to densities using home-range data from GPS tracking. We also calculated relative abundance indices from the same data. Key results The CMR methods produced credible estimates of the change in population abundance, with useful confidence intervals, showing a statistically identifiable population decline from at least 0.7 cats km–2 before trapping down to 0.4 cats km–2 after trapping. The indexing method also showed a statistically identifiable decrease in abundance. Conclusions Camera-trapping and CMR methods can provide a useful method for monitoring changes in the absolute abundance of feral cat populations. Camera-trap data may also be used to produce indices of relative abundance when the assumptions of CMR models cannot be met. Implications These methods are widely applicable. The ability to reliably estimate feral cat abundances allows for more effective management than is generally available.

Estimating and indexing feral cat population abundances using camera traps

In less than a century the ecological profile of koalas on Kangaroo Island has shifted from that of a species introduced for conservation purposes to one of pest status. Between 1923 and 1925, 18 koalas were released on Kangaroo Island. Their numbers increased rapidly and in 1997 a population-control program was implemented based on a population estimate of 5000 koalas. During the course of this program, it became clear that the koala population on Kangaroo Island was much greater and more widely distributed than previously thought, hence a more comprehensive population survey was carried out. In 2000–01 the koala population size was calculated using a stratified sampling approach based on five 'catchment units' and three habitat classifications that were known to support koalas. The koala population was estimated to be ~27 000 koalas in 2001. There were substantial differences in koala density in the low-, medium- and high-quality habitat within each catchment unit, and therefore large differences in the spatial distribution of koalas across Kangaroo Island. This revised population estimate has substantial ramifications for the Kangaroo Island Koala Management Program that was set in place in 1997.

Pip Masters

Papers

Long-term dynamics of rodent populations in arid Australia: the influence of rainfall

A continental‐scale analysis of feral cat diet in Australia

The effects of fire-driven succession and rainfall on small mammals, in Spinifex grassland at Uluru National Park, Northern Territory

Estimating and indexing feral cat population abundances using camera traps

Koalas on Kangaroo Island: from introduction to pest status in less than a century