Comparative patterns of winter habitat use by muskoxen and caribou in northern Alaska

Thesis (M.S.) University of Alaska Fairbanks, 1992Snow depth and hardness strongly influenced selection of feeding zones, (i.e., those areas used for foraging), in late winter by both muskoxen (Ovibos moschatus) and caribou (Rangifer tarandus grand) in northern Alaska. Snow in feeding zones was shallower and softer than in surrounding zones. Depth of feeding craters was less than the average snow depth in feeding zones. Moist sedge tundra types were used most often by muskoxen, and their diet, based on microhistological analysis of feces, was dominated by graminoids. Moist sedge and Dryas tundra types were most often used by caribou; lichens and evergreen shrubs were the major constituents of their diet. Despite selection of moist sedge tundra types by both muskoxen and caribou in late winter, dietary and spatial overlap was minimal

A comparison of faecal analysis with backtracking to determine the diet composition and species preference of the black rhinoceros (Diceros bicornis minor)

The diet of black rhinoceros (Diceros bicornis minor) was studied using backtracking and faecal analysis in South Africa. Both methods yielded different results, with a large bias for dominant species. Results of backtracking showed that the rhinos browsed on 80 plant species. Grasses comprised 4.5% of the diet in the faecal analysis, but were not recorded during the backtracking. The backtracking method, along with a measure of forage availability, was used to identify two groups of plant species, those species taken in a higher proportion than available in the field and those taken in a lower proportion. Chemical analyses showed that these two species groups were similar in in vitro digestibility, macro-elements and fibre constituents. Mean bite size and species contribution to the diet were not correlated with any of the forage quality parameters, indicating that rhinos were not maximising nutrient intake or minimising fibre intake of these consumed plant species

The Influence of Predator-Prey Population Dynamics on the Long-term Evolution of Food Web Structure

We develop a set of equations to describe the population dynamics of many interacting species in food webs. Predator-prey interactions are non-linear, and are based on ratio-dependent functional responses. The equations account for competition for resources between members of the same species, and between members of different species. Predators divide their total hunting/foraging effort between the available prey species according to an evolutionarily stable strategy (ESS). The ESS foraging behaviour does not correspond to the predictions of optimal foraging theory. We use the population dynamics equations in simulations of the Webworld model of evolving ecosystems. New species are added to an existing food web due to speciation events, whilst species become extinct due to coevolution and competition. We study the dynamics of species-diversity in Webworld on a macro-evolutionary timescale. Coevolutionary interactions are strong enough to cause continuous overturn of species, in contrast to our previous Webworld simulations with simpler population dynamics. Although there are significant fluctuations in species diversity because of speciation and extinction, very large scale extinction avalanches appear to be absent from the dynamics, and we find no evidence for self-organised criticality.Comment: 40 pages, preprint forma

Busted by the bite

Large herbivores are charismatic species known to engineer ecosystems through a variety of effects. Conflicts can sometimes arise when these effects are undesirable. However, without detailed knowledge on herbivore selectivity for landscapes, patches and plants, these positive and negative effects remain difficult to predict. Such species and sex-specific selectivity have inherent evolutionary and ecological mechanisms. In order to study such mechanisms it is important to study the partitioning of resources at multiple scales. Most studies have looked at large-scale resource partitioning (such as movement patterns) but fewer study the fine-scale levels of selectivity such as the individual bites taken by herbivores. This level of detail is, however, important because it is essentially the direct mechanism through which ecosystem effects are manifested. Specifically for the browsing herbivore guild, such fine-scale studies have largely been impractical due to forested habitats which limit direct observation of behaviors. DNA-based diagnostics are becoming more and more popular within ecology as they provide vital data to answer certain questions. In this thesis I developed two versions of a method to differentiate between five species of large herbivore browsers using trace amounts of environmental DNA left at browsed twigs. The first version uses a traditional amplification method for identifying the species of browsers and the second uses an advanced and more sensitive method for identifying the species and sex of browsers. Using environmental DNA, I determined species-specific browsing patterns across three studies. I found overall that traditional methods for attributing browsing at the species level tend to be misleading. In one study I show that although one species may be blamed for forest plantation damages, DNA evidence showed a partitioning between three herbivore species. I also document the partitioning of plant parts among different sized ungulates and show that overlap in browsing heights and bite diameters is much larger than previously assumed. In another study I experimentally verified the selectivities of free-ranging herbivores for three species of trees. This thesis thus not only develops new molecular ecological tools but also provides new insights into resource partitioning and hence the ecosystem effects of herbivores

Rates of agonism among female primates: a cross-taxon perspective

Agonism is common in group-living animals, shaping dominance relationships and ultimately impacting individual tness. Rates of agonism vary considerably among taxa, however, and explaining this variation has been central in ecological models of female social relationships in primates. Early iterations of these models posited a link to diet, with more frequent agonism predicted in frugivorous species due to the presumed greater contestability of fruits relative to other food types. Although some more recent studies have suggested that dietary categories may be poor predictors of contest competition among primates, to date there have been no broad, cross-taxa comparisons of rates of female–female agonism in relation to diet. This study tests whether dietary variables do indeed pre- dict rates of female agonism and further investigates the role of group size (i.e., number of competitors) and substrate use (i.e., degree of arboreality) on the frequency of agonism. Data from 44 wild, unprovisioned groups, including 3 strepsirhine species, 3 platyrrhines, 5 colobines, 10 cercopithecines, and 2 hominoids were analyzed using phylogenetically controlled and uncontrolled methods. Results indicate that diet does not predict agonistic rates, with trends actually being in the opposite direction than predicted for all taxa except cercopithecines. In contrast, agonistic rates are positively associated with group size and possibly degree of terrestriality. Competitor density and perhaps the risk of ghting, thus, appear more important than general diet in predicting agonism among female primates. We discuss the implications of these results for socio-ecological hypotheses

Size dimorphism and sexual segregation in pheasants: tests of three competing hypotheses (article)

This is the final version. Available from PeerJ via the DOI in this record.The dataset associated with this article is in ORE at: https://doi.org/10.24378/exe.683Fine scale sexual segregation outside of the mating season is common in sexually dimorphic and polygamous species, particularly in ungulates. A number of hypotheses predict sexual segregation but these are often contradictory with no agreement as to a common cause, perhaps because they are species specific. We explicitly tested three of these hypotheses which are commonly linked by a dependence on sexual dimorphism for animals which exhibit fine-scale sexual segregation; the Predation Risk Hypothesis, the Forage Selection Hypothesis, and the Activity Budget Hypothesis, in a single system the pheasant, Phasianus colchicus; a large, sedentary bird that is predominantly terrestrial and therefore analogous to ungulates rather than many avian species which sexually segregate. Over four years we reared 2,400 individually tagged pheasants from one day old and after a period of 8–10 weeks we released them into the wild. We then followed the birds for 7 months, during the period that they sexually segregate, determined their fate and collected behavioural and morphological measures pertinent to the hypotheses. Pheasants are sexually dimorphic during the entire period that they sexually segregate in the wild; males are larger than females in both body size and gut measurements. However, this did not influence predation risk and predation rates (as predicted by the Predation Risk Hypothesis), diet choice (as predicted by the Forage Selection Hypothesis), or the amount of time spent foraging, resting or walking (as predicted by the Activity Budget Hypothesis). We conclude that adult sexual size dimorphism is not responsible for sexual segregation in the pheasant in the wild. Instead, we consider that segregation may be mediated by other, perhaps social, factors. We highlight the importance of studies on a wide range of taxa to help further the knowledge of sexual segregation.The work was jointly funded by the University of Exeter, the Game and Wildlife Conservation Trust and an ERC Consolidator Award (616474) awarded to Joah R. Madden

Explaining prehistoric variation in the abundance of large prey: a zooarchaeological analysis of deer and rabbit hunting along the Pecho Coast of Central California

journal articleThree main hypotheses are commonly employed to explain diachronic variation in the relative abun dance of remains of large terrestrial herbivores: (1) large prey populations decline as a function of anthro pogenic overexploitation; (2 ) large prey tends to increase as a result of increasing social payoffs; and (3) proportions of large terrestrial prey are dependent on stochastic fluctuations in climate. This paper tests predictions derived from these three hypotheses through a zooarchaeological analysis of eleven temporal components from three sites on central California's Pecho Coast. Specifically, we examine the trade offs between hunting rabbits (Sylvilagus spp.) and deer (Odocoileus hemionus) using models derived from human behavioral ecology. The results show that foragers exploited a robust population of deer through out most of the Holocene, only doing otherwise during periods associated w ith climatic trends unfavor able to larger herbivores. The most recent component (Late Prehistoric/Contact era) shows modest evidence of localized resource depression and perhaps greater social benefits from hunting larger prey; we suggest that these final changes resulted from the introduction of bow and arrow technology. Overall, results suggest that along central California's Pecho Coast, density independent factors described as cli matically mediated prey choice best predict changes in the relative abundance of large terrestrial herbi vores through the Holocene

Sexual segregation in moose: effects of incisor morphology, quality of willows, and foraging behavior

Thesis (M.S.) University of Alaska Fairbanks, 2002Differences in the jaw morphology of Alaskan moose (Alces alces gigas) may relate to sexual segregation. Male Alaskan moose had significantly wider incisor breadths than did females; however, incisor depth did not differ between sexes. Those differences in jaw architecture might relate to the diets of sexes when they are spatially segregated. Moose consume willow (Salix spp.) as a fundamental component of their diet. Smaller-diameter twigs were more digestible, had more protein, and contained less fiber than larger-diameter twigs. Conversely, no relation existed between age of twigs and digestibility. Ruminants may segregate spatially because females competitively exclude males. An experiment on foraging behavior, however, rejected that hypothesis. Nonetheless, females fed more selectively and had higher rates of forage intake than did males. Thus, differences in foraging behavior between the sexes still may relate to sexual segregation