Victoria J. Bakker

SCALE-DEPENDENT PATTERNS IN BODY SIZE DISTRIBUTIONS OF NEOTROPICAL MAMMALS

We report on the spatial scaling of body size distributions in the mammalian fauna of South America, exclusive of fully aquatic or volant species. Although the frequency distribution of body sizes for 720 species of South American mammals was qualitatively similar to that observed for 464 species of North American mammals, different patterns emerged at smaller spatial scales in these two regions. At smaller scales in North America, body size frequency distributions became progressively more uniform on a log axis, whereas they remained modal with decreasing spatial scale in neotropical rain forest, and the mode shifted to larger body sizes. This unexpected scaling relationship appears to reflect the addition of a substantial third habitat dimension: the rain forest canopy. When rain forest mammals were separated by foraging stratum (terrestrial, scansorial, and arboreal), distributions of body sizes within strata exhibited scaling relationships similar to those observed in temperate areas of North and South America. These results are consistent with earlier interpretations of body size scaling across large geographic or taxonomic ranges, but they emphasize the pivotal role that habitat structure and heterogeneity can play in the ecological and evolutionary development of faunas. Additionally, these results underscore the role of habitat complexity as a factor contributing to the latitudinal gradient in species richness.

Incorporating Ecological Drivers and Uncertainty into a Demographic Population Viability Analysis for the Island Fox

Biometricians have made great strides in the generation of reliable estimates of demographic rates and their uncertainties from imperfect field data, but these estimates are rarely used to produce detailed predictions of the dynamics or future viability of at-risk populations. Conversely, population viability analysis (PVA) modelers have increased the sophistication and complexity of their approaches, but most do not adequately address parameter and model uncertainties in viability assessments or include important ecological drivers. Merging the advances in these two fields could enable more defensible predictions of extinction risk and better evaluations of management options, but only if clear and interpretable PVA results can be distilled from these complex analyses and outputs. Here, we provide guidance on how to successfully conduct such a combined analysis, using the example of the endangered island fox (Urocyon littoralis), endemic to the Channel Islands of California, USA. This more rigorous demographic PVA was built by forming a close marriage between the statistical models used to estimate parameters from raw data and the details of the subsequent PVA simulation models. In particular, the use of mark-recapture analyses and other likelihood and information-theoretic methods allowed us to carefully incorporate parameter and model uncertainty, the effects of ecological drivers, density dependence, and other complexities into our PVA. Island fox populations show effects of density dependence, predation, and El Nino events, as well as substantial unexplained temporal variation in survival rates. Accounting not only for these sources of variability, but also for uncertainty in the models and parameters used to estimate their strengths, proved important in assessing fox viability with different starting population sizes and predation levels. While incorporating ecological drivers into PVA assessments can help to predict realistic dynamics, we also show that unexplained process variance has important effects even in our extremely well-studied system, and therefore must not be ignored in PVAs. Overall, the treatment of causal factors and uncertainties in parameter values and model structures need not result in unwieldy models or highly complex predictions, and we emphasize that future PVAs can and should include these effects when suitable data are available to support their analysis.

Population viability management: ecological standards to guide adaptive management for rare species.

Many approaches to rare species management formulated by academics lack practicality and meaning for managers. Here, we propose an approach, which we refer to as population viability management (PVM), that is based on linking monitoring and management models with population models. By closely coordinating biological analyses with the range of decisions and actions considered by managers, the PVM approach ensures that population models reflect realistic management options and risk tolerances, and that adaptive conservation systems remain focused on population viability rather than statistical targets indirectly tied to population persistence. We summarize our use of PVM to formulate draft recovery criteria for the endangered island fox and to generate specific guidance for conserving this species. We argue that PVM can be widely adapted to provide more biologically justified and focused management and monitoring recommendations than those typically emerging from conventional population viability analyses. ...

Evaluating the Potential Effectiveness of Compensatory Mitigation Strategies for Marine Bycatch

Conservationists are continually seeking new strategies to reverse population declines and safeguard against species extinctions. Here we evaluate the potential efficacy of a recently proposed approach to offset a major anthropogenic threat to many marine vertebrates: incidental bycatch in commercial fisheries operations. This new approach, compensatory mitigation for marine bycatch (CMMB), is conceived as a way to replace or reduce mandated restrictions on fishing activities with compensatory activities (e.g., removal of introduced predators from islands) funded by levies placed on fishers. While efforts are underway to bring CMMB into policy discussions, to date there has not been a detailed evaluation of CMMBs potential as a conservation tool, and in particular, a list of necessary and sufficient criteria that CMMB must meet to be an effective conservation strategy. Here we present a list of criteria to assess CMMB that are tied to critical ecological aspects of the species targeted for conservation, the range of possible mitigation activities, and the multi-species impact of fisheries bycatch. We conclude that, overall, CMMB has little potential for benefit and a substantial potential for harm if implemented to solve most fisheries bycatch problems. In particular, CMMB is likely to be effective only when applied to short-lived and highly-fecund species (not the characteristics of most bycatch-impacted species) and to fisheries that take few non-target species, and especially few non-seabird species (not the characteristics of most fisheries). Thus, CMMB appears to have limited application and should only be implemented after rigorous appraisal on a case-specific basis; otherwise it has the potential to accelerate declines of marine species currently threatened by fisheries bycatch.

MICROHABITAT FEATURES INFLUENCE THE MOVEMENTS OF RED SQUIRRELS (TAMIASCIURUS HUDSONICUS) ON UNFAMILIAR GROUND

Abstract Little is known about the behavior of mammals moving on unfamiliar ground, yet this information could be critical to assessing and enhancing landscape connectivity. I investigated the movements of adult red squirrels (Tamiasciurus hudsonicus) on unfamiliar ground to determine if squirrels selected specific microhabitat features and if manipulations of preferred features influenced movement choices. Rather than selecting for cover from predators or territorial conspecifics, 25 squirrels released outside their home ranges used microhabitat features that appeared to allow rapid, efficient, and inconspicuous travel (logs, open vegetation, low slopes, and high shrub cover per stem) while maintaining proximity to arboreal escape routes. Similarly, in 73 trials with 55 individuals, squirrels released in experimental plots moved preferentially through areas of greater log cover and cover per stem. Manipulating microhabitat features in plots within forested habitat enhanced red squirrel movements, underscoring the possibility of altering microhabitats in 2nd-growth forests or corridors to increase landscape connectivity for forest-associated mammals.

Proactive Conservation Management of an Island-endemic Bird Species in the Face of Global Change

Biodiversity conservation in an era of global change and scarce funding benefits from approaches that simultaneously solve multiple problems. Here, we discuss conservation management of the island scrub-jay (Aphelocoma insularis), the only island-endemic passerine species in the continental United States, which is currently restricted to 250-square-kilometer Santa Cruz Island, California. Although the species is not listed as threatened by state or federal agencies, its viability is nonetheless threatened on multiple fronts. We discuss management actions that could reduce extinction risk, including vaccination, captive propagation, biosecurity measures, and establishing a second free-living population on a neighboring island. Establishing a second population on Santa Rosa Island may have the added benefit of accelerating the restoration and enhancing the resilience of that islands currently highly degraded ecosystem. The proactive management framework for island scrub-jays presented here illustrates how strategies for species protection, ecosystem restoration, and adaptation to and mitigation of climate change can converge into an integrated solution.

The Use of Surrogate Data in Demographic Population Viability Analysis: A Case Study of California Sea Lions

Reliable data necessary to parameterize population models are seldom available for imperiled species. As an alternative, data from populations of the same species or from ecologically similar species have been used to construct models. In this study, we evaluated the use of demographic data collected at one California sea lion colony (Los Islotes) to predict the population dynamics of the same species from two other colonies (San Jorge and Granito) in the Gulf of California, Mexico, for which demographic data are lacking. To do so, we developed a stochastic demographic age-structured matrix model and conducted a population viability analysis for each colony. For the Los Islotes colony we used site-specific pup, juvenile, and adult survival probabilities, as well as birth rates for older females. For the other colonies, we used site-specific pup and juvenile survival probabilities, but used surrogate data from Los Islotes for adult survival probabilities and birth rates. We assessed these models by comparing simulated retrospective population trajectories to observed population trends based on count data. The projected population trajectories approximated the observed trends when surrogate data were used for one colony but failed to match for a second colony. Our results indicate that species-specific and even region-specific surrogate data may lead to erroneous conservation decisions. These results highlight the importance of using population-specific demographic data in assessing extinction risk. When vital rates are not available and immediate management actions must be taken, in particular for imperiled species, we recommend the use of surrogate data only when the populations appear to have similar population trends.

Moving forward with effective goals and methods for conservation: a reply to Marvier and Kareiva

We welcome the added nuance that Marvier and Kareiva have included in their response [1] to our analysis [2] of New Conservation Science (NCS). However, we take issue with multiple points that they raise. In particular, we do not believe that our arguments in any way ‘pit good values against each other’ or that we have painted conservation to date as a string of unqualified success stories. Nonetheless, we are glad that they now appear to embrace many of the same fundamental goals, strategies, and motivations that have long characterized conservation.

On the Fast Track to Recovery: Island Foxes on the Northern Channel Islands

Abstract. The island fox (Urocyon littoralis) represents an unusual case of a species that achieved virtual recovery a mere 15 years after population declines were first discovered. Island fox subspecies on San Miguel, Santa Rosa, and Santa Cruz islands declined precipitously in the mid-1990s due to predation by Golden Eagles (Aquila chrysaetos), which had not historically bred on the islands. In 2008, a 10-year period of recovery action implementation ended. The recovery program had included captive breeding and reintroduction of island foxes and capture and relocation of Golden Eagles. Free-ranging fox populations have been monitored to assess recovery of each subspecies and to detect potential threats of disease and predation. Monitoring included (1) annual grid trapping to allow estimation of annual population size via capture-mark-recapture methods and (2) systematic surveillance of radio-collared foxes to allow estimation of mortality rates and causes. A comprehensive demographic modeling effort produced a population recovery tool that uses adult mortality and population size estimates from the monitoring programs to estimate extinction risks for each fox population. The tool allows managers to assess when threats are sufficiently mitigated to consider populations acceptably safe from extinction. Population monitoring indicates that island foxes on the northern Channel Islands have increased up to 30-fold from population lows and that annual survival has been 90% or better in most years. The San Miguel and Santa Cruz subspecies have approached or reached predecline population levels, and application of the recovery tool indicates they will be biologically recovered by 2013. Biological recovery of the Santa Rosa subspecies, hindered by predation which caused lower survival in 2010, will occur by 2017.

SEROLOGIC SURVEY OF THE ISLAND SPOTTED SKUNK ON SANTA CRUZ ISLAND

Abstract Two rare endemic carnivores occur on Californias northern Channel Islands: island spotted skunks (Spilogale gracilis amphiala) and island foxes (Urocyon littoralis). As insular carnivores, both may be particularly vulnerable to novel pathogens. We tested sera from 31 island spotted skunks on Santa Cruz Island, where both skunks and foxes occur sympatrically, to establish their exposure to disease agents. One skunk (3%) tested positive for canine heartworm, and 3 skunks (10%) tested positive for canine parvovirus. None showed evidence of exposure to canine adenovirus, canine distemper virus, canine herpesvirus, Leptospira bacteria (serovars pomona, canicola, and icterohaemorrhagiae), or pseudorabies virus. Spotted skunks on Santa Cruz Island apparently have low susceptibility or exposure to these pathogens and are unlikely to be reservoirs of these diseases for island foxes.