William T. Bean

Accelerated Human Population Growth at Protected Area Edges

Protected areas (PAs) have long been criticized as creations of and for an elite few, where associated costs, but few benefits, are borne by marginalized rural communities. Contrary to predictions of this argument, we found that average human population growth rates on the borders of 306 PAs in 45 countries in Africa and Latin America were nearly double average rural growth, suggesting that PAs attract, rather than repel, human settlement. Higher population growth on PA edges is evident across ecoregions, countries, and continents and is correlated positively with international donor investment in national conservation programs and an index of park-related funding. These findings provide insight on the value of PAs for local people, but also highlight a looming threat to PA effectiveness and biodiversity conservation.

The Rise of the Mesopredator

Apex predators have experienced catastrophic declines throughout the world as a result of human persecution and habitat loss. These collapses in top predator populations are commonly associated with dramatic increases in the abundance of smaller predators. Known as “mesopredator release,” this trophic interaction has been recorded across a range of communities and ecosystems. Mesopredator outbreaks often lead to declining prey populations, sometimes destabilizing communities and driving local extinctions. We present an overview of mesopredator release and illustrate how its underlying concepts can be used to improve predator management in an increasingly fragmented world. We also examine shifts in North American carnivore ranges during the past 200 years and show that 60% of mesopredator ranges have expanded, whereas all apex predator ranges have contracted. The need to understand how best to predict and manage mesopredator release is urgent—mesopredator outbreaks are causing high ecological, economic, and social costs around the world.

Species distribution models of an endangered rodent offer conflicting measures of habitat quality at multiple scales

Summary 1. The high cost of directly measuring habitat quality has led ecologists to test alternate methods for estimating and predicting this critically important ecological variable. In particular, it is frequently assumed but rarely tested that models of habitat suitability (‘species distribution models’, SDMs) may provide useful indices of habitat quality, either from an individual animal or manager’s perspective. Critically, SDMs are increasingly used to estimate species’ ranges, with an implicit assumption that areas of high suitability will result in higher probability of persistence. This assumption underlies efforts to use SDMs to design protected areas, assess the status of cryptic species or manage responses to climate change. Recent tests of this relationship have provided mixed results, suggesting SDMs may predict abundance but not other measures of high-quality habitat (e.g. survival, persistence). 2. In this study, we created a suite of SDMs for the endangered giant kangaroo rat Dipodomys ingens at three distinct scales using the machine-learning method Maxent. We compared these models with three measures of habitat quality: survival, abundance and body condition. 3. Species distribution models were not correlated with survival, while models at all scales were positively correlated with abundance. Finer-scale models were more closely correlated with abundance than the largest scale. Body condition was not correlated with habitat suitability at any scale. The inability of models to predict survival may be due to a lack of information in environmental covariates; unmeasured community processes or stochastic events; or the inadequacy of using models that predict species presence to also predict demography. 4. Synthesis and applications. Species distribution models (SDMs), especially fine scale ones, may be useful for longer-term management goals, such as identifying high-quality habitat for protection. However, short-term management decisions should be based only on models that use covariates appropriate for the necessary temporal and spatial scales. Assumptions about the relationship between habitat suitability and habitat quality must be made explicit. Even then, care should be taken in inferring multiple types of habitat quality from SDMs.

ENVIRONMENTAL REVIEWS AND CASE STUDIES: Applications of Unmanned Aircraft Systems (UAS) for Waterbird Surveys

Utilizing unmanned aircraft systems (UAS) can be an efficient and repeatable means of surveying wildlife, especially waterbirds. As with any technology in its infancy, case studies offer opportunities to explore drawbacks and limitations, both anticipated and unanticipated. We examined the relationship between flight altitude and camera focal length on bird identification. We then conducted a post-hoc analysis to examine the effect of flight altitude on bird flushing behavior. We flew UAS missions at three locations in California and Nevada to assess the use of UAS for censusing non-nesting waterbirds. A minimum pixel resolution of approximately 5 mm was needed be able to identify most waterbird species from imagery. Sensors needed to be carefully calibrated in order to obtain images of sufficient quality to identify waterbirds over open water. Our results suggest that gas-powered UAS may result in increased rates of flushing at low flight altitudes for some waterbirds. With careful design of surveys and processing workflow, UAS show promise for censusing and monitoring waterbirds.

A multi-scale distribution model for non-equilibrium populations suggests resource limitation in an endangered rodent.

Species distributions are known to be limited by biotic and abiotic factors at multiple temporal and spatial scales. Species distribution models, however, frequently assume a population at equilibrium in both time and space. Studies of habitat selection have repeatedly shown the difficulty of estimating resource selection if the scale or extent of analysis is incorrect. Here, we present a multi-step approach to estimate the realized and potential distribution of the endangered giant kangaroo rat. First, we estimate the potential distribution by modeling suitability at a range-wide scale using static bioclimatic variables. We then examine annual changes in extent at a population-level. We define “available” habitat based on the total suitable potential distribution at the range-wide scale. Then, within the available habitat, model changes in population extent driven by multiple measures of resource availability. By modeling distributions for a population with robust estimates of population extent through time, and ecologically relevant predictor variables, we improved the predictive ability of SDMs, as well as revealed an unanticipated relationship between population extent and precipitation at multiple scales. At a range-wide scale, the best model indicated the giant kangaroo rat was limited to areas that received little to no precipitation in the summer months. In contrast, the best model for shorter time scales showed a positive relation with resource abundance, driven by precipitation, in the current and previous year. These results suggest that the distribution of the giant kangaroo rat was limited to the wettest parts of the drier areas within the study region. This multi-step approach reinforces the differing relationship species may have with environmental variables at different scales, provides a novel method for defining “available” habitat in habitat selection studies, and suggests a way to create distribution models at spatial and temporal scales relevant to theoretical and applied ecologists.

Ecological winners and losers of extreme drought in California

An unprecedented era of climatic volatility is altering ecosystems across our planet1. The potential scale, pace and consequences of this global change have been modelled extensively2, yet little empirical research has quantified the impacts of extreme climate events on the composition of contemporary ecological communities. Here, we quantified the responses of 423 sympatric species of plants, arthropods, birds, reptiles and mammals to California’s drought of 2012–2015—the driest period in the past 1,200 years3 for this global biodiversity hotspot. Plants were most responsive to one-year water deficits, whereas vertebrates responded to longer-term deficits, and extended drought had the greatest impact on carnivorous animals. Locally rare species were more likely to increase in numbers and abundant species were more likely to decline in response to drought, and this negative density dependence was remarkably consistent across taxa and drought durations. Our system-wide analysis reveals that droughts indirectly promote the long-term persistence of rare species by stressing dominant species throughout the food web. These findings highlight processes that shape community structure in highly variable environments and provide insights into whole-community responses to modern climate volatility.California’s 2012–2015 drought is shown to have altered community structure (plants, arthropods, birds, reptiles and mammals), indirectly promoting the long-term persistence of rare species by stressing dominant ones.

Seasonal resource acquisition strategies of a facultative specialist herbivore at the edge of its range

Understanding animal performance at range edges has gained increasing interest due to climate change, but most efforts have focused on specialist species. Studying the breadth and plasticity of generalist resource acquisition strategies will provide important insight into how mammals adapt to and persist under a variety of environmental conditions. The North American porcupine (Erethizon dorsatum) is a widely distributed generalist herbivore with special adaptations to harsh climates and low-quality diets. However, on the north coast of California, which has a mild climate and abundant vegetation, porcupine populations are patchily distributed and may be in decline. We studied seasonal resource use of porcupines in a coastal dune ecosystem by measuring changes in body mass, home range size, habitat selection, and diet. Both female and male porcupines lost body mass between summer and winter (= 8.3% and 17.2%, respectively), although less than reported elsewhere. Their home range sizes were 31% larger during summer than winter. Porcupines selected swales and marshes during the summer, when they fed primarily on willow leaves, and switched to conifer forests and coastal scrub during winter, when they fed on bark, conifer needles, and leaves of evergreen shrubs. Porcupines exploited 2 novel food sources common in Pacific coastal lowlands: coast manroot fruits and California wax myrtle leaves. We suggest that porcupines employ a similarly flexible resource acquisition strategy across their range, and although it appears to be broadly effective, they may face challenges from plant phenology, low broad-leaved tree diversity, and high winter precipitation in Pacific coastal climates.

A Suitability Model for White-Footed Voles with Insights into Habitat Associations at the Southern Boundary of Their Range

Abstract The White-footed Vole (Arborimus albipes) is one of the least-studied small mammals in North America. Most reported occurrence data come from incidental captures from larger trapping efforts and have demonstrated a strong affinity for Red Alder (Alnus rubra) trees. Recent research represented a range expansion in western Oregon, but little is known about the species at the southern end of its range in California. We developed a distribution model for the species to identify areas best targeted for additional White-footed Vole research. We used this model to survey by trapping in Humboldt and Del Norte Counties, California, and documented 3 new occurrences for the species. These 3 occurrences were incorporated into a final distribution model. This model suggests the possibility of White-footed Vole occurrence in southern Humboldt and northern Mendocino Counties, which would represent a southern expansion of their range. White-footed Voles were captured in areas with smaller alders than non-capture areas, supporting work from Oregon that suggests the species may not be tied to older stands as had been previously reported. Targeted trapping and physiological studies could clarify the environmental niche of this vole.