Interspecific Asymmetries in Behavioral Plasticity Drive Seasonal Patterns of Temporal Niche Partitioning in an Island Carnivore Community.

Animals vary considerably in the amount of behavioral plasticity they exhibit in daily activity timing and temporal niche switching. It is not well understood how environmental factors drive changes in temporal activity or how interspecific differences in the plasticity of activity timing ultimately manifest in free-living animals. Here, we investigated the temporal structure and organization of activity patterns of two insular mammalian carnivores living in sympatry, the island fox (Urocyon littoralis) and island spotted skunk (Spilogale gracilis amphiala). Using collar-mounted accelerometers, we assessed the plasticity of behavioral activity rhythms in foxes and skunks by investigating how environmental factors drive the distribution of locomotor activity across the day and year, and subsequently examined the dynamics of temporal niche overlap between the two species. We documented that foxes express phenotypic plasticity in daily activity timing across the year, ranging from nocturnal to diurnal to crepuscular rhythms depending on the individual and time of year. Most notably, foxes increased the proportion of daytime activity as seasonal temperatures decreased. Overall, activity patterns of foxes were consistent with the circadian thermoenergetics hypothesis, which posits that animals that switch their patterns of activity do so to coincide with the most energetically favorable time of day. In contrast to foxes, skunks exhibited little behavioral plasticity, appearing strictly nocturnal across the year. While the duration of skunk activity bouts increased with the duration of night, timing of activity onset and offset extended into daytime hours during summer when the duration of darkness was shortest. Analysis of temporal niche overlap between foxes and skunks suggested that niche overlap was highest during summer and lowest during winter and was dictated primarily by temporal niche switching in foxes, rather than skunks. Collectively, our results highlight how interspecific asymmetries in behavioral plasticity drive dynamic patterns of temporal niche overlap within an island carnivore community.

Responses to terrestrial nest predators by endemic and introduced Hawaiian birds.

Birds free from nest predators for long periods may either lose the ability to recognize and respond to predators or retain antipredator responses if they are not too costly. How these alternate scenarios play out has rarely been investigated in an avian community whose members have different evolutionary histories. We presented models of two nest predators (rat and snake) and a negative control (tree branch) to birds on Hawai'i Island. Endemic Hawaiian birds evolved in the absence of terrestrial predators until rats were introduced approximately 1,000 years ago. Introduced birds evolved with diverse predator communities including mammals and snakes, but since their introduction onto the island approximately one century ago have been free from snake predation. We found that (a) endemic and introduced birds had higher agitation scores toward the rat model compared with the branch, and (b) none of the endemic birds reacted to the snake model, while one introduced bird, the Red-billed Leiothrix (Leiothrix lutea), reacted as strongly to the snake as to the rat. Overall, endemic and introduced birds differ in their response to predators, but some endemic birds have the capacity to recognize and respond to introduced rats, and one introduced bird species retained recognition of snake predators from which they had been free for nearly a century, while another apparently lost that ability. Our results indicate that the retention or loss of predator recognition by introduced and endemic island birds is variable, shaped by each species' unique history, ecology, and the potential interplay of genetic drift, and that endemic Hawaiian birds could be especially vulnerable to introduced snake predators.

Ecological Potential for Rabies Virus Transmission via Scavenging of Dead Bats by Mesocarnivores.

Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the source of spillover infections into mesocarnivore species. Although rabies transmission generally is assumed to occur via bite, laboratory studies have demonstrated the potential for rabies transmission via ingestion of rabid animals. We investigated the ecological potential for this mode of transmission by assessing mesocarnivore scavenging behavior of dead bats in suburban habitats of Flagstaff, Arizona, US. In autumn 2013, summer 2014, and autumn 2015, we placed 104 rabies-negative bat carcasses either near buildings, in wildland areas, or in residential yards and then monitored them with trail cameras for 5 d. Overall, 52 (50%) bat carcasses were scavenged, with 39 (75%) of those scavenged by striped skunks ( Mephitis mephitis ). Within our study area, striped skunks had a higher ecological potential to contract rabies via ingestion of bat carcasses compared to other mesocarnivore species, due both to a greater number of encounters and a higher probability of ingestion per encounter (91%), and they were significantly more likely to approach bat carcasses in yards than in wildland areas. Raccoons ( Procyon lotor ) and gray foxes ( Urocyon cinereoargenteus ) had fewer encounters (nine and 13, respectively) and lower probability of ingesting bats (33% and 8%, respectively).

Disparity in population structuring of Southwestern Willow Flycatchers based on geographic distance, movement patterns, and genetic analyses.

Estimates of population connectivity often are based on demographic analysis of movements among subpopulations, but this approach may fail to detect rare migrants or overestimate the contribution of movements into populations when migrants fail to successfully reproduce. We compared movement data of endangered Southwestern Willow Flycatchers among isolated populations in Nevada and Arizona from 1997 to 2008 to genetic analyses of samples collected between 2004 and 2008 to determine the degree to which these two methods were concordant in their estimates of population structuring. Given that documented movements of 13 color-banded adults and 23 juveniles over 10 years indicated low rates of long-distance movements, we predicted that genetic analyses would show significant population structuring between a northern (Nevada) deme and a southern (Arizona) deme. We genotyped 93 adult individuals at seven microsatellite loci and used two Bayesian clustering programs, STRUCTURE and GENELAND, to predict population structure. Both clustering algorithms produced the same structuring pattern; a cluster containing birds breeding in Pahranagat National Wildlife Refuge, the northern-most Nevada site, and a cluster comprised of all other populations. These results highlight that estimates of subpopulation connectivity based on demographic analyses may differ from those based on genetics, suggesting either temporal changes in the pattern of movements, the importance of undetected movements, or differential contribution of migrants to the subpopulations they enter.

Terrestrial vertebrates alter seedling composition and richness but not diversity in an Australian tropical rain forest.

Although birds and mammals play important roles in several mechanisms hypothesized to maintain plant diversity in species-rich habitats, there have been few long-term, community-level tests of their importance. We excluded terrestrial birds and mammals from fourteen 6 x 7.5 m plots in Australian primary tropical rain forest and compared recruitment and survival of tree seedlings annually over the subsequent seven years to that on nearby open plots. We re-censused a subset of the plots after 13 years of vertebrate exclusion to test for longer-term effects. After two years of exclusion, seedling abundance was significantly higher (74%) on exclosure plots and remained so at each subsequent census. Richness was significantly higher on exclosure plots from 1998 to 2003, but in 2009 richness no longer differed, and rarefied species richness was higher in the presence of vertebrates. Shannon's diversity and Pielou's evenness did not differ in any year. Vertebrates marginally increased density-dependent mortality and recruitment limitation, but neither effect was great enough to increase richness or diversity on open plots relative to exclosure plots. Terrestrial vertebrates significantly altered seedling community composition, having particularly strong impacts on members of the Lauraceae. Overall, our results highlight that interactions between terrestrial vertebrates and tropical tree recruitment may not translate into strong community-level effects on diversity, especially over the short-term, despite significant impacts on individual species that result in altered species composition.

Nightly and seasonal movements, seasonal home range, and focal location photo-monitoring of urban striped skunks (Mephitis mephitis): implications for rabies transmission.

We followed radio-collared striped skunks (Mephitis mephitis) from January 2004-December 2005 in two urban areas of Flagstaff, Arizona, USA to determine seasonal patterns of movement and home-range size. We also used automated cameras to determine the potential for inter- and intraspecific interaction at skunks' diurnal resting sites and nocturnal focal locations. We found no difference between sexes in nightly rates of travel or in size of seasonal home range. Nightly rates of travel were greatest in the postbreeding months (May-July) and smallest from November to February, consistent with larger home ranges (95% kernel estimates) from March-August and smaller home ranges from September-February. Sixty-three percent of monitored males and 38% of monitored females crossed the urban-wildland interface, in at least one direction on at least one night, and some remained outside the urban area for days or weeks, indicating that skunks could act as vectors of disease across the urban-wildland interface. We recorded co-occurrence of skunks with domestic cats (Felis domesticus), raccoons (Procyon lotor), gray foxes (Urocyon cinereoargenteus), and other skunks at focal locations and diurnal retreats used by skunks, suggesting these areas are potential sites for both inter- and intraspecific rabies transmission and could be targeted by wildlife managers during trapping or vaccination programs.

Functional and numerical responses of predators: where do vipers fit in the traditional paradigms?

Snakes typically are not considered top carnivores, yet in many ecosystems they are a major predatory influence. A literature search confirmed that terrestrial ectotherms such as snakes are largely absent in most discussions of predator-prey dynamics. Here, we review classical functional and numerical responses of predator-prey relationships and then assess whether these traditional views are consistent with what we know of one group of snakes (true vipers and pitvipers: Viperidae). Specifically, we compare behavioural and physiological characteristics of vipers with those of more commonly studied mammalian (endothermic) predators and discuss how functional and numerical responses of vipers are fundamentally different. Overall, when compared to similar-sized endotherms, our analysis showed that vipers have: (i) lower functional responses owing primarily to longer prey handling times resulting from digestive limitations of consuming large prey and, for some adults, tolerance of fasting; (ii) stronger numerical responses resulting from higher efficiency of converting food into fitness currency (progeny), although this response often takes longer to be expressed; and (iii) reduced capacity for rapid numerical responses to short-term changes in prey abundance. Given these factors, the potential for viperids to regulate prey populations would most likely occur when prey populations are low. We provide suggestions for future research on key issues in predator-prey relationships of vipers, including their position within the classical paradigms of functional and numerical responses.

Seed-caching responses to substrate and rock cover by two Peromyscus species: implications for pinyon pine establishment.

We examined whether pinyon mice ( Peromyscus truei) and brush mice ( P. boylii) could act as directed dispersal agents of pinyon pine ( Pinus edulis) through differential responses to soil particle size and rock cover. In field experiments, we allowed mice to either cache pinyon seeds or recover artificially cached seeds (pilfer) from quadrats containing large- or small-particle soils. Both species placed most (70%) seed caches in small-particle soil. Pilfering was the same from both particle sizes in the first year, while more seeds were pilfered from large-particle soils in the second year. In separate experiments, rock cover interacted with soil particle size, with both species placing over 50% of their caches in small-particle soil with rock cover. Overall, we found greater seed-caching in small-particle soils near rocks, with equal or lower pilfering from small-particle soils, suggesting more seeds would survive in small-particle soils near rock cover. Three lines of evidence supported the hypothesis that mice could act as directed dispersers by moving pinyon seeds to beneficial microsites for germination and establishment. First, in greenhouse experiments, pinyon seed germination was 4 times greater in small-particle soil cores than in large-particle soil cores. Second, soils near rocks had significantly higher water content than areas of open soil at the driest time of the year, a critical factor for seedling survival in the arid southwestern USA. Third, 75% of juvenile pinyon trees were growing in small-particle soils, and 45% were growing near rock nurses.