Structure in vital rates, internal source-sink dynamics, and their influence on current population expansion for the feral horses (Equus ferrus caballus) of Sable Island, Nova Scotia

Population-level dynamics are affected by temporal variation in individual vital rates of survival and reproduction, which are in turn influenced by habitat-specific processes. Variation in habitat quality within a population’s range can drive movement of individuals between different areas, and so there may be a relationship between variation in vital rates and spatial heterogeneity in population growth (λ). I investigated this relationship for the feral horses (Equus ferus caballus) of Sable Island, Nova Scotia, Canada, from 2008−2010. The horses (n = 484 in September 2010) form a closed population that is free from human interference and predation. I analyzed annual population growth using age-structured projection matrix models parameterized with survival and fertility data collected from almost every female (98.7% of females). I found some evidence of temporal variation in growth during the two years I studied the population (λ2008−2009 = 1.065, λ2009−2010 = 1.117). Age structure appears to have converged to a stable age distribution, suggesting this growth rate has been sustained in the years leading up to the end of my study. Variation in vital rates of adult fertility and foal survival made the largest contribution to annual variation in population growth. Future growth is predicted to be most influenced by proportional changes in adult survival, which remained relatively unchanged between 2008 and 2010. The population can be stratified into three spatially distinct subunits found across a west−east longitudinal gradient of water resources (access to permanent ponds vs. ephemeral water sources and holes dug in sand). I assessed the existence of source-sink dynamics to determine if individual movements between subunits could explain spatial heterogeneity in population growth. I found that spatial heterogeneity in growth appears to be most influenced by immigration and emigration events between subunits. Evidence suggests that current growth of the overall Sable Island horse population is made possible by individual emigration from more productive into less productive subunits; in particular, a source presented in the west of the island where permanent water ponds are located

How nestling tree swallows (Tachycineta bicolor) integrate their responses to hunger and signalling by nestmates

Young animals in a broad range of taxa solicit care from their parents with begging displays, which are used at least partly for competition among brood or litter mates. The effect of other begging offspring on an individual’s own begging display varies across studies, however, increasing its intensity in some, but not changing, or even decreasing it, in others. One possible reason for this discrepancy is that the potential pay-off for more intense begging depends not only on how intensely an individual’s brood or littermates are begging, but also on how long that individual has been without food. Surprisingly, however, no studies have focused on how begging responses vary when both factors are varied simultaneously. We therefore examined how nestling tree swallows, Tachycineta bicolor, respond to nestmates in relation to both their own hunger levels and the begging intensity of nestmates. During a period of food deprivation, we played focal nestlings parental contact calls either alone (control) or with the begging calls of a nestling deprived of food for 30–50 (low intensity) or 100–110 min (high intensity). Nestlings called for longer in response to the low-intensity playback, but, surprisingly, not in the high-intensity playback, in which they instead delayed the onset of their calling. All these responses to nestmates were independent of how long the responding nestling had been deprived of food. Thus, even in the seemingly intensely competitive environment of a passerine brood, offspring do not necessarily respond to nestmates with escalation. This may be because de-escalation is the best competitive option in some circumstances, or because begging has other functions besides advertisement of individual need and competition over food allocation. Certainly, the results illustrate the need for studies of how nestmate interactions vary across a broad range of contexts

Increasing density leads to generalization in both coarse-grained habitat selection and fine-grained resource selection in a large mammal

Summary 1. Density is a fundamental driver of many ecological processes including habitat selection. Theory on density-dependent habitat selection predicts that animals should be distributed relative to profitability of habitat, resulting in reduced specialization in selection (i.e. generalization) as density increases and competition intensifies. 2. Despite mounting empirical support for density-dependent habitat selection using isodars to describe coarse-grained (interhabitat) animal movements, we know little of how density affects fine-grained resource selection of animals within habitats [e.g. using resource selection functions (RSFs)]. 3. Using isodars and RSFs, we tested whether density simultaneously modified habitat selection and within-habitat resource selection in a rapidly growing population of feral horses (Equus ferus caballus Linnaeus; Sable Island, Nova Scotia, Canada; 42% increase in population size from 2008 to 2012). 4. Among three heterogeneous habitat zones on Sable Island describing population clusters distributed along a west-east resource gradient (west-central-east), isodars revealed that horses used available habitat in a density-dependent manner. Intercepts and slopes of isodars demonstrated a pattern of habitat selection that first favoured the west, which generalized to include central and east habitats with increasing population size consistent with our understanding of habitat quality on Sable Island. 5. Resource selection functions revealed that horses selected for vegetation associations similarly at two scales of extent (total island and within-habitat zone). When densities were locally low, horses were able to select for sites of the most productive forage (grasslands) relative to those of poorer quality. However, as local carrying capacity was approached, selection for the best of available forage types weakened while selection for lower-quality vegetation increased (and eventually exceeded that of grasslands). 6. Isodars can effectively describe coarse-grained habitat selection in large mammals. Our study also shows that the main predictions of density-dependent habitat selection are highly relevant to our interpretation of RSFs in space and time. At low but not necessarily high population size, density will be a leading indicator of habitat quality. Fitness maximization from specialist vs. generalist strategies of habitat and resource selection may well be apparent at multiple spatial extents and grains of resolution

Local-scale assessment of regional conservation plans : strategies for the conservation of animals and plants in a tropical rainforest and surrounding mixed-farmland

There is an urgent need to conserve biodiversity in human-modified landscapes throughout the tropics. Animal conservation has traditionally focused on single species, but it remains unclear whether these strategies will also protect other taxa that co-occur within the ecosystem. These uncertainties can also affect plant conservation if management interventions change plant-animal interactions. I identified steps to mitigate the effects of hunting, forest product extraction, and farming on rainforest animals and plants in Suaka Margasatwa Buton Utara (SMBU) and the surrounding mixed-farmland on Buton Island, Southeast Sulawesi, Indonesia. First, I used Bayesian Network inference to assess whether protecting anoa (Bubalus spp.) habitat might also benefit other animals by modelling species co-occurrences in relation to habitat and human activities. Next, I completed a pantropical Network Meta-Analysis (NMA) to identify where controlling the foraging of granivorous mammals might reduce mortality of management-sowed seeds in human-modified forests. Finally, I used the NMA to guide an experimental assessment of how seed predation might affect the regeneration of nine plant species in the reserve and mixed-farmland. Buton macaques (Macaca ochreata) did not co-occur with anoa and were the only species to avoid human-dominated areas. The government might consider concentrating patrols in easy-to-access areas to increase the distribution of macaques throughout SMBU and the mixed-farmland. The NMA identified that granivore control could help reduce seed mortality, but which seeds to protect depended on the type of human activity that modified the forest. At SMBU, granivore control was not required in the mixed-farmland because seed predation was very low for 78% of the studied plants. Low seed losses in the mixed-farmland suggested that forest regeneration might be enhanced by increasing macaque distribution and natural seed rain throughout those areas. My approach could be used to design projects that conserve animals and plants in human-modified ecosystems. Local co-occurrence analyses can identify species that remain vulnerable to humans under conservation projects focused on other species. In data deficient situations, wide-scale evidence synthesis using NMA can help guide decision making, such as when to use granivore control, in human-modified ecosystems.Science, Faculty ofZoology, Department ofGraduat

Graphical results of a <i>K</i>-means analysis indicating the appropriate number of clusters of water source-groupings, based on within-groups sum of squares as a function of the number of clusters from hierarchical cluster analysis of points of water use (<i>n</i> = 122), for the analysis of water availability to the Sable Island horses, 2008–2010.

<p>The first obvious bend indicates the appropriate number of groups (i.e., 3).</p

Habitat features, water, percent cover, and abundance of indicator species for three island areas, from west to east, on Sable Island, Canada, (August 2010).

a<p>Abundance measured on a 0–16 presence/absence scale per plot.</p

Density and population growth characteristics of female horses in areas 1, 2, and 3 (west to east) on Sable Island, Canada (June–September 2008–2010).

a<p>Arithmetic mean.</p>b<p>Annualized population growth calculated as geometric mean.</p

Study area and longitudinal gradient in sources of fresh water for feral horses on Sable Island, Canada, 2008–2010.

<p>(a) Sources of water (<i>n</i> = 122) grouped according to hierarchical cluster analysis, with area 1 containing only permanent ponds (triangles); area 2 containing permanent ponds and horse-excavated wells (circles); and area 3 containing only excavated wells. (b) Boundaries for areas 1, 2, and 3 that include clusters of water sources and the exclusive movements of females using those water sources.</p

Comparison of the annual count in summer (August) of females of all age classes for areas 1, 2, and 3 (west to east) from 2008 to 2010, Sable Island, Canada.

<p>Comparison of the annual count in summer (August) of females of all age classes for areas 1, 2, and 3 (west to east) from 2008 to 2010, Sable Island, Canada.</p

Comparison of the mean abundance of sandwort <i>Honckenya peploides</i> (right-side-up triangle) and beach pea <i>Lathyrus japonicas</i> (upside-down triangle) with percent cover for vegetated plots (open circle) in areas 1, 2, and 3 (west to east) on Sable Island, Canada, 2010.

<p> <b>Error bars are ±1 SE.</b></p