Foraging theory upscaled: the behavioural ecology of herbivore movement

Abstract

We outline how principles of optimal foraging developed for diet and food patch selection might be applied to movement behaviour expressed over larger spatial and temporal scales. Our focus is on large mammalian herbivores, capable of carrying global positioning system (GPS) collars operating through the seasonal cycle and dependent on vegetation resources that are fixed in space but seasonally variable in availability and nutritional value. The concept of intermittent movement leads to the recognition of distinct movement modes over a hierarchy of spatio-temporal scales. Over larger scales, periods with relatively low displacement may indicate settlement within foraging areas, habitat units or seasonal ranges. Directed movements connect these patches or places used for other activities. Selection is expressed by switches in movement mode and the intensity of utilization by the settlement period relative to the area covered. The type of benefit obtained during settlement periods may be inferred from movement patterns, local environmental features, or the diel activity schedule. Rates of movement indicate changing costs in time and energy over the seasonal cycle, between years and among regions. GPS telemetry potentially enables large-scale movement responses to changing environmental conditions to be linked to population performance.

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“…While generalist species may exhibit flexibility by having a greater diet breadth and broader geographical range, specialist species are often more vulnerable because they may have a limited diet and spatial distribution that may increase their risk of extinction (Clavel et al 2011;Slayter et al 2013;Ducatez et al 2015). Foraging strategies of such specialist species are a central focus of study in animal ecology due to their influence on habitat selection, home range, social interactions, reproduction, and population regulation (Goss-Custard et al 1995;Owen-Smith et al 2010).…”

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“…Scales of interaction are an important determinant of the behavioural descriptions that are used within individual models (Taylor, 1976;Gustine et al, 2006;Owen-Smith et al, 2010). Stochastic methods have been used to describe behavioural variation (Stephens and Charnov, 1982;Marion et al, 2005).…”

“…This paper has reviewed research progress and direction in determining nutritional preferences of free-grazing herbivores. Knowing where a herbivore is and what it is doing is only part of the story; this needs to be supported by more detailed information on what the animal is doing within the nutritional landscape (Owen-Smith et al, 2010).Although current field-based intake methods provide opportunities to test the effect of experimentally imposed treatments on intake and the nutritional status of grazing herbivores in relatively simple grazing systems over short time periods, in more complex systems understanding behavioural preferences and adaptation is the basis for understanding the nutritional environment. The integration of a broader range of environmental and behavioural factors in the context of herbivore nutrition is characterized by a shift from a focus on nutritional physiology to nutritional ecology.…”

“…Correlating location information with nutrient selection requires data that can be used to derive grazing behaviour. The hierarchy of herbivore foraging behaviour spans spatial and temporal scales from bites per second through to regional migration occurring over years (Bailey et al, 1996;Owen-Smith et al, 2010). A number of studies have attempted to use location information derived from GPS data to determine herbivore behaviour (Ungar et al, 2005; Buerkert and Schlecht, 2009;Ganskopp and Bohnert, 2009).…”

“…If herbivore movement is to be reliably mapped onto the spatial distribution of nutrient resources, then higher sample rate location data will be required to ensure sufficient spatial accuracy for smaller-scale interactions (Schick et al, 2008;Montgomery et al, 2010). Within herbivore studies, there has been an overwhelming focus on patch-and bite-level nutrient selection preferences (OwenSmith et al, 2010); there are significant opportunities to explore large-scale (regional and over several years) nutrient selection preferences within extensive livestock production systems (Hebblewhite and Haydon, 2010;Owen-Smith et al, 2010).It is beyond the scope of this paper to provide a detailed review of vegetation assessment methods. However, there have been a number of recent studies that have integrated detailed spatial on-ground assessments with herbivore location data to derive preference indices and they demonstrate potential future research direction.…”