Integrating sensory ecology and predator-prey theory to understand animal responses to fire

Fire regimes are changing dramatically worldwide due to climate change, habitat conversion, and the suppression of Indigenous landscape management. Although there has been extensive work on plant responses to fire, including their adaptations to withstand fire and long-term effects of fire on plant communities, less is known about animal responses to fire. Ecologists lack a conceptual framework for understanding behavioural responses to fire, which can hinder wildlife conservation and management. Here, we integrate cue-response sensory ecology and predator-prey theory to predict and explain variation in if, when and how animals react to approaching fire. Inspired by the literature on prey responses to predation risk, this framework considers both fire-naïve and fire-adapted animals and follows three key steps: vigilance, cue detection and response. We draw from theory on vigilance tradeoffs, signal detection, speed-accuracy tradeoffs, fear generalization, neophobia and adaptive dispersal. We discuss how evolutionary history with fire, but also other selective pressures, such as predation risk, should influence animal behavioural responses to fire. We conclude by providing guidance for empiricists and outlining potential conservation applications.     

Population genetics of the American eel (Anguilla rostrata): FST = 0 and North Atlantic Oscillation effects on demographic fluctuations of a panmictic species

We performed population genetic analyses on the American eel (Anguilla rostrata) with three main objectives. First, we conducted the most comprehensive analysis of neutral genetic population structure to date to revisit the null hypothesis of panmixia in this species. Second, we used this data to provide the first estimates of contemporary effective population size (N_e) and to document temporal variation in effective number of breeders (N_b) in American eel. Third, we tested for statistical associations between temporal variation in the North Atlantic Oscillation (NAO), the effective number of breeders and two indices of recruit abundance. A total of 2142 eels from 32 sampling locations were genotyped with 18 microsatellite loci. All measures of differentiation were essentially zero, and no evidence for significant spatial or temporal genetic differentiation was found. The panmixia hypothesis should thus be accepted for this species. N_b estimates varied by a factor of 23 among 12 cohorts, from 473 to 10 999. The effective population size N_e was estimated at 10 532 (95% CI, 9312–11 752). This study also showed that genetically based demographic indices, namely N_b and allelic richness (Ar), can be used as surrogates for the abundance of breeders and recruits, which were both shown to be positively influenced by variation during high (positive) NAO phases. Thus, long‐term genetic monitoring of American glass eels at several sites along the North American Atlantic coast would represent a powerful and efficient complement to census monitoring to track demographic fluctuations and better understand their causes.     

Disproportionately large ecological role of a recently mass-culled flying fox in native forests of an oceanic island

Human-wildlife conflicts pose a growing threat to many species worldwide and require increasingly innovative and multi-disciplinary resolutions. Because of their apparent simplicity and political appeal, lethal approaches like culling are often favoured, decisions to cull are typically poorly supported by scientific evidence and the limitations and drawbacks of culls minimised. As natural habitats decline and fruit crop production expands, fruit-eating bats in the Old World (family Pteropodidae) are increasingly in conflict with fruit farmers. This conflict is exemplified on Mauritius where the government has implemented two mass culls of a threatened flying fox (Pteropus niger) since 2015 in response to fruit-grower concerns. The culls and illegal hunting reduced the bat population by >50%. In this context, we sought to investigate the ecological role and service provided by the targeted flying fox through seed dissemination to gauge what may be lost as the species becomes rarer or extinct. We randomly sampled the woody native community in six of the best-preserved moist-to-wet native forests of Mauritius using 90 plots of 100 m² each and identified and measured the stem size of all woody plants ≥1 cm in diameter. Species were classified by whether their fruits occur in the diet of the flying fox in an exclusive, confirmed or likely manner and we assumed that fruit consumption is equivalent to potential seed dissemination. The relative importance of these three categories to the total woody plant community was then quantified as the proportion of species richness, stem density and basal area (as a surrogate of biomass) that they represent. We also investigated whether the main traits of species (seed size, fruit size, and maximum stem diameter) vary among bat-dispersal categories and differ from those of species whose fruits are not currently known to be eaten by the flying fox. On average, although about a quarter of the native woody species (24.6%) have fruits confirmed as eaten and seeds dispersed by the flying fox, these species comprise about half (53.1%) of the stems sampled and the majority (63.1%) of the basal area of native woody plant in the island’s native forests. About half of that latter biomass figure comprises species for which the flying fox is the exclusive native vertebrate frugivore and seed disperser. Plants disseminated by the flying fox are typically large trees with large fruit and seeds. These trees are often key components of the canopy, therefore fulfilling structural engineer roles that provide resources and conditions for the survival of many forest species. The flying fox plays a disproportionally large ecological role in maintaining forest structure and biodiversity in the long-term. Consequently, lethal approaches to the conflict with fruit-farmers threaten not only an endangered species, but ecological processes central to the viability of native forests. Our findings highlight the importance of including the ecological costs of culling in decision-making processes intended to resolve human-wildlife conflicts.     

The human–primate interface in the New Normal: Challenges and opportunities for primatologists in the COVID-19 era and beyond

The emergence of SARS-CoV-2 in late 2019 and human responses to the resulting COVID-19 pandemic in early 2020 have rapidly changed many aspects of human behavior, including our interactions with wildlife. In this commentary, we identify challenges and opportunities at human–primate interfaces in light of COVID-19, focusing on examples from Asia, and make recommendations for researchers working with wild primates to reduce zoonosis risk and leverage research opportunities. First, we briefly review the evidence for zoonotic origins of SARS-CoV-2 and discuss risks of zoonosis at the human–primate interface. We then identify challenges that the pandemic has caused for primates, including reduced nutrition, increased intraspecific competition, and increased poaching risk, as well as challenges facing primatologists, including lost research opportunities. Subsequently, we highlight opportunities arising from pandemic-related lockdowns and public health messaging, including opportunities to reduce the intensity of problematic human–primate interfaces, opportunities to reduce the risk of zoonosis between humans and primates, opportunities to reduce legal and illegal trade in primates, new opportunities for research on human–primate interfaces, and opportunities for community education. Finally, we recommend specific actions that primatologists should take to reduce contact and aggression between humans and primates, to reduce demand for primates as pets, to reduce risks of zoonosis in the context of field research, and to improve understanding of human–primate interfaces. Reducing the risk of zoonosis and promoting the well-being of humans and primates at our interfaces will require substantial changes from “business as usual.” We encourage primatologists to help lead the way.     

Quantification of prior impact in terms of effective current sample size

Bayesian methods allow borrowing of historical information through prior distributions. The concept of prior effective sample size (prior ESS) facilitates quantification and communication of such prior information by equating it to a sample size. Prior information can arise from historical observations; thus, the traditional approach identifies the ESS with such a historical sample size. However, this measure is independent of newly observed data, and thus would not capture an actual “loss of information” induced by the prior in case of prior-data conflict. We build on a recent work to relate prior impact to the number of (virtual) samples from the current data model and introduce the effective current sample size (ECSS) of a prior, tailored to the application in Bayesian clinical trial designs. Special emphasis is put on robust mixture, power, and commensurate priors. We apply the approach to an adaptive design in which the number of recruited patients is adjusted depending on the effective sample size at an interim analysis. We argue that the ECSS is the appropriate measure in this case, as the aim is to save current (as opposed to historical) patients from recruitment. Furthermore, the ECSS can help overcome lack of consensus in the ESS assessment of mixture priors and can, more broadly, provide further insights into the impact of priors. An R package accompanies the paper.     

Abundance and diversity of rodents at the human–wildlife interface in Western Serengeti, Tanzania

Rodent species abundance and diversity in Western Serengeti are evaluated and discussed in relation to different levels of conservation status [Unprotected Area (UA), Game Reserve (GR) and National Park (NP)] and broad site differences in human livelihood activities. A total of 2170 individuals, spread over 16 rodent species, were caught in a capture‐mark‐recapture study which covered both the dry and wet seasons. The more humid site (Tabora B) in the northern part of Serengeti had the highest diversity of rodents followed by the Mihale site at the western extension. The driest site at Robanda had the lowest overall species diversity. Diversity also varied between the three levels of conservation status whereby the UA had the least diversity while the NP, which enjoyed the highest level of conservation status, had the highest diversity of rodents. Unprotected Area and NP plots at Tabora B showed a rodent species similarity index of 40%; all the other paired plots scored over 50% similarity indices, suggesting that, within a site, species composition did not vary significantly between the three levels of conservation status. The Robanda site had the highest (56%) overall abundance of rodents; Mihale and Tabora B sites had about the same level of rodent abundance (20 and 24% respectively). For the Mihale site, Mastomys natalensis ranked first followed by Arvicanthis niloticus and Tatera robusta, each of which contained 40, 38 and 16%, respectively, of all individuals caught at the site. For the Robanda site, the figures were 66%A. niloticus, 22%M. natalensis and 9%T. robusta; while for the Tabora B site the scores were 37%M. natalensis, 18%T. robusta and 11%Lemniscomys barbarus. The differences in diversity, species composition and population abundance appear to result largely from physiognomic vegetation types, and habitat perturbations caused by livelihood activities in Western Serengeti.     

Social Eavesdropping: A Game-Theoretic Analysis

Here we extend the classic Hawk-Dove model of animal conflict to allow for continuous variation in fighting strengths. Whereas the winner of a fight is chosen at random in the discrete game, in our continuous game, the winner of any fight is the stronger individual, and costs are higher for more evenly matched opponents. We identify the evolutionary stable strength threshold beyond which an animal should be prepared to engage in aggressive behaviour and show that this threshold increases with variance in fighting strength when the costs of aggression are insensitive to the level of strength asymmetry, but decreases with variance when the costs are sensitive to the level of asymmetry. In contrast to the classic discrete game, population-wide aggressive behaviour occurs only when the costs of fighting are zero. It is now known that animals can eavesdrop on the outcome of contests between neighbours and modify their behaviour towards observed winners and losers. We therefore further extend our model to allow for social eavesdropping within networks comprising three individuals. Whereas earlier work showed that eavesdropping increases the frequency of mutually aggressive contests in the discrete game by enhancing the value of victory, here we show that aggression thresholds in the continuous game are always higher with eavesdropping than without it: for sufficiently weak animals, avoiding the costs of challenging an observed winner over-rides the potential benefit of winning, so that eavesdropping reduces the frequency of aggressive encounters. Thus, even though strength is not directly observable, information is extracted from the variation in fighting ability that the classic Hawk-Dove game ignores.     

Habitat Use of Fox Squirrels in an Urban Environment

Abstract: Tree squirrels are one of the most familiar mammals found in urban areas and are considered both desirable around homes and, conversely, a pest. We examined fox squirrel (Sciurus niger) habitat use in inner city and suburban areas using radiotelemetry. We estimated habitat selection ratios at differing scales by season and fox squirrel activity. Telemetry data suggests that during periods of inactivity radiocollared fox squirrels (n = 82) selected 1) areas with greater tree canopy, 2) live oaks (Quercus fusiromis and Q. virginiana), and 3) trees with larger diameters and canopies. When inactive during the winter and spring, fox squirrels also preferred, within their core areas, to use the inside of buildings, and during periods of activity in the autumn and spring, fox squirrels preferred grassy areas. During periods of activity, fox squirrels avoided using pavement but did not exclude it from their core-area movements. Fox squirrels' ability to use buildings and to tolerate pavement in core-area movements make vast areas of the urban environment available to fox squirrels. In evaluating habitat variables that increased fox squirrel activity in urban areas, we found the number of large and medium trees, amount of pavement and grassy areas, canopy cover, number of oaks, and the area covered by buildings were all important factors in predicting fox squirrel activity in an urban environment. Our data suggests urban planners, animal damage control officials, wildlife managers, and landscapers who want to control urban fox squirrel populations through habitat manipulation should consider the reduction of oaks trees, a reduction of the canopy cover, and restricting the access of fox squirrels to buildings. Alternatively, home owners and squirrel enthusiasts hoping to bolster fox squirrel populations in urban areas should consider increasing the number of large mast—bearing trees and canopy cover and providing nest boxes.     

Nuptial gift consumption influences female remating in a scorpionfly: male or female control of mating rate?

In the scorpionfly Panorpa cognata, males provide females with saliva secretions as nuptial food gifts. Consequently, females derive material benefits and possibly also genetic benefits from multiple matings. Females therefore generally should have a high motivation to remate. Males, on the other hand, do not share this interest, which will generate a sexual conflict over remating interval, possibly leading to male adaptations that prevent females from remating with other males. In this study, I found that mated females were less prone to copulate than virgin females, despite female benefits of multiple matings. Further, I found that the remating interval was significantly longer if the first copulation was long compared to shorter matings. This effect does not entirely depend on copulation duration per se, but on the amount of saliva, that a female is consuming during copulation. These results suggest a mating-induced refractory period and can be interpreted as male manipulation of female remating behaviour mediated through substances in the nuptial gift. Alternatively, receiving large nuptial gifts may decrease the prospective direct fitness benefits from further copulations, and thus change optimal female remating rate. Furthermore, gift size has been shown to correlate with male nutritional condition, which may be an indicator of male genetic quality. Females may therefore benefit indirectly by not remating following copulations involving large saliva gifts. In this scenario, female remating interval would be an effect of cryptic female choice.     

Is there empirical evidence for the cost of begging?

Offspring should demand more food than the optimal amount for the parents to bring (parent–offspring conflict), and models on the evolution of parent–offspring communication suggest that an equilibrium is reached when the costs associated with begging make it unprofitable for the offspring to increase its level of begging. Empirical evidence for this cost, however, is mixed, and the conclusions of most of authors are that begging is inexpensive. In this study, the existing empirical evidence for this cost is reviewed. One cost proposed is the attraction of predators due to begging calls, but empirical support for this cost is low. However, studies performed cannot dismiss such a cost. Another possible cost is the metabolic expenditure, but empirical evidence for this cost is mixed, with some works contending that it is low, while others deem it important. Other possible metabolic costs have not been studied. A loss of inclusive fitness may be an important cost for the evolution of begging, and robust empirical evidence does exist for this cost. Costs associated with brood reduction also are reviewed. In conclusion, there is not enough empirical evidence to test the models on the evolution of begging. Most costs proposed have not yet been studied or the approach used has been insufficient to reject the null hypothesis (i.e., absence of cost).