Insights for caribou/reindeer management using optimal foraging theory

Optimal foraging theory is useful to wildlife managers, because it helps explain the nutritional value of different habitats for wildlife species. Based upon nutritional value, the use of different habitats can be predicted, including how factors such as insect harassment, predation and migration might modify habitat selection. If habitat value and use can be understood, then changes in habitat availability which are of concern to wildlife managers can be assessed. The theory is used to address diet choice and habitat use of caribou/reindeer. Diet choice is examined in terms of lichen composition of the diet and is demonstrated to be a function of daily feeding time, food abundance and digestive capacity. The diet choice model is then used to assess the nutritional profitability of different habitats and which habitat should be preferred based upon nutritional profitability. Caribou/reindeer use of habitats is demonstrated to be easily modified by insect harassment and predation which change the nutritional profitability of habitats differentially. The same type of approach could be used to explain migratory behaviour; however, the needed parameter values are unavailable. The results of this analysis lead one to question some common conceptions about caribou/reindeer ecology

Food Plant Selection by a Generalist Herbivore: The Moose

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/119078/1/ecy19816241020.pd

Fire and grazing in a mesic tallgrass prairie: impacts on plant species and functional traits

Fire is a globally distributed disturbance that impacts terrestrial ecosystems and has been proposed to be a global “herbivore.” Fire, like herbivory, is a top-down driver that converts organic materials into inorganic products, alters community structure, and acts as an evolutionary agent. Though grazing and fire may have some comparable effects in grasslands, they do not have similar impacts on species composition and community structure. However, the concept of fire as a global herbivore implies that fire and herbivory may have similar effects on plant functional traits. Using 22 years of data from a mesic, native tallgrass prairie with a long evolutionary history of fire and grazing, we tested if trait composition between grazed and burned grassland communities would converge, and if the degree of convergence depended on fire frequency. Additionally, we tested if eliminating fire from frequently burned grasslands would result in a state similar to unburned grasslands, and if adding fire into a previously unburned grassland would cause composition to become more similar to that of frequently burned grasslands. We found that grazing and burning once every four years showed the most convergence in traits, suggesting that these communities operate under similar deterministic assembly rules and that fire and herbivory are similar disturbances to grasslands at the trait-group level of organization. Three years after reversal of the fire treatment we found that fire reversal had different effects depending on treatment. The formerly unburned community that was then burned annually became more similar to the annually burned community in trait composition suggesting that function may be rapidly restored if fire is reintroduced. Conversely, after fire was removed from the annually burned community trait composition developed along a unique trajectory indicating hysteresis, or a time lag for structure and function to return following a change in this disturbance regime. We conclude that functional traits and species-based metrics should be considered when determining and evaluating goals for fire management in mesic grassland ecosystems

Hunter-gatherer foraging: A linear programming approach

A linear program model is developed to examine how much effort hunter-gatherers should devote to hunting vs gathering. This foraging model contains a foraging time, a digestive capacity, and a nutritional constraint which determine the optimal solution to a given human foraging goal: nutritional maximization, foraging time minimization, risk aversion, or food storage maximization. The model is compared with the most commonly used foraging models in anthropology and is shown to be more appropriate for hunter-gatherers. Using data on present day hunter-gatherers, the model's solution is shown to indicate quantitatively that these people tend to either maximize their energy or protein intake rather than minimize their time spent providing for their energy and protein needs. The model also predicts diet proportions, absolute food intake, time spent foraging, and sexual division of labor. A general version of the model is developed where the hunting and gathering cropping rates are made functions of environmental primary production. The solutions to this model agree with world patterns of hunter-gatherer diets, foraging time, and sexual division of labor. Modifications of the model to investigate risk-averse foraging and food storage are also presented, and the model is applied to determine when agriculture/pastoralism might be adopted and how hunter-gatherer body size might be selected. Although the model appears closely to predict observed hunter-gatherer foraging, the model's sensitivity and the quality of the data available make its uncritical acceptance unwarranted at this time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26778/1/0000334.pd

Optimal activity times and habitat choice of moose

A set of concepts was presented which could be used to model an animal's activity cycle and habitat choice as an optimization process. The model was applied to moose ( Alces alces ) summer activity and its predictions were consistent with observed feeding times and habitat selections. The optimization model had a goal of maximizing daily feeding time at the least possible energetic cost. This goal was consistent with a foraging strategy that maximized the intake of some nutritional component, i.e. energy, protein, etc. The optimization problem, however, was bounded. Three constraints appeared to limit the goal: body temperature must be maintained within set upper and lower limits, thermal equilibrium must be maintained over an extended period so the activity cycle strategy can be repeated and sufficient time must be spent ruminating.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47735/1/442_2004_Article_BF00346984.pd

An optimal foraging-based model of hunter-gatherer population dynamics

Population changes for hunter-gatherers are modeled on the basis of nutritional intake, which is determined using an optimal foraging model based upon the optimization technique of linear programming. The population model not only demonstrates how hunter-gatherer demography changes with nutrition, but also shows how their density influences food abundance in the environment which in turn affects their nutritional status. Differences in food availability in different environments can be assessed by examining the effects of different preexploitation maxima for food abundances. Hunter-gatherer populations are predicted by the model to display a stable limit cycle which varies in severity with the maximum food abundance in the environment, being more severe at very low and high food abundances. Observed hunter-gatherer densities, growth rates, and life expectancies are shown to be consistent with the population model's predictions for different environments. The model is also used to examine the impact huntergatherers might have on their food resources including whether or not overexploitation (extinction) occurs and how their diets change in different environments with changes in population density. Finally, the model is used to examine archaeological questions about the Paleo-Indian colonization of the New World and the effects of technological innovation by hunter-gatherers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27038/1/0000026.pd

Effects of spines and thorns on Australian arid zone herbivores of different body masses

We investigated the effects of thorns and spines on the feeding of 5 herbivore species in arid Australia. The herbivores were the rabbit ( Oryctolagus cuniculus ), euro kangaroo ( Macropus robustus ), red kangaroo ( Macropus rufus ), sheep ( Ovis aries ), and cattle ( Bos taurus ). Five woody plants without spines or thorns and 6 woody plants with thorns were included in the study. The spines and thorns were not found to affect the herbivores' rates of feeding (items ingested/min), but they did reduce the herbivores' rates of biomass ingestion (g-dry/item). The reduction in biomass ingested occurred in two ways: at a given diameter, twigs with spines and thorns had less mass than undefended plants, and the herbivores consumed twigs with smaller diameters on plants with spines and thorns. The relative importance of the two ways that twigs with spines and thorns provided less biomass varied with herbivore body mass. Reduced twig mass was more important for small herbivores, while large herbivores selected smaller diameters. The effectiveness of spines and thorns as anti-herbivore defenses did not vary with the evolutionary history of the herbivores (i.e. native vs. introduced). Spines and thorns mainly affected the herbivores' selection of maximum twig sizes (reducing diameter and mass), but the minimum twig sizes selected were also reduced.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47795/1/442_2004_Article_BF00317715.pd