Herbivore population regulation and resource heterogeneity in a stochastic environment

Hempson, Gareth P.; Illius, A.W.; Hendricks, Howard; Bond, William J.; Vetter, Susanne

doi:10.1890/14-1501.1

Cited by 37 publications

(30 citation statements)

References 41 publications

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“…Although less pronounced than in our case, carry‐over effects from maternal winter condition to offspring survival have also been reported for other northern ungulates, including moose Alces alces (Milner et al ), red deer Cervus elaphus (Kruuk et al ) and bighorn sheep Ovis canadensis (Festa‐Bianchet et al ). This strong link between maternal energy stores and reproductive output contrasts the findings in typically income dependent species like roe deer Capreolus capreolus (Andersen et al , Plard et al ) and goats Capra hircus (Hempson et al ), where annual recruitment is highly dependent upon resource availability during the postnatal period.…”

Section: Discussionmentioning

confidence: 66%

Maternal winter body mass and not spring phenology determine annual calf production in an Arctic herbivore

Veiberg

Loe

Albon

et al. 2016

Oikos

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Warming of the Arctic has resulted in earlier snowmelt and green-up of plants in spring, potentially disrupting the synchrony between plant phenology and breeding phenology in herbivores. A negative relationship between offspring survival in West Greenland caribou and the timing of vegetation emergence was the first finding of such a mismatch in Arctic mammals. However, other studies indicate that the energy for foetal growth and early lactation is predominantly drawn from stored energy reserves typical of 'capital' breeders, suggesting that conditions well before spring influence calf production more than the timing of spring onset. Here we use 20 years of observations of marked Svalbard reindeer to evaluate determinants of annual recruitment, as measured by the presence of a calf at foot in mid-summer. Spring temperatures and the enhanced vegetation index were used as proxies for spring onset, while data on body mass and pregnancy rates in late winter allowed us to determine maternal condition and the reproductive status before spring. Pregnancy rate, offspring survival and annual recruitment were all strongly correlated with average late winter adult female body mass (r  0.87; r  0.83; r  0.92, respectively). Contrary to the findings in West Greenland, neither early calf survival nor annual recruitment were correlated with the two measures of annual variation in spring phenology (r  -0.07, p  0.8 and r  -0.15, p  0.6, respectively). We also revisit the Greenland data and reveal that the pattern of covariance between early and late measures of fecundity, as well as between early measures of fecundity and offspring survival, correspond with the results from Svalbard. Our results emphasize that conditions affecting maternal body mass during winter explain close to all the variation in recruitment, questioning the importance of the role of a mismatch between plant phenology and calving date.

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Section: Discussionmentioning

confidence: 66%

Maternal winter body mass and not spring phenology determine annual calf production in an Arctic herbivore

Veiberg

Loe

Albon

et al. 2016

Oikos

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“…The key resource concept was strongly supported in a study of semi‐arid South African rangeland (Hempson, Illius, Hendricks, Bond, & Vetter, 2015). Livestock (goats) body condition followed a density‐dependent depletion of the very limited dry‐season riverine vegetation—a key resource area—and annual demographic parameters of the animals tracked dry‐season forage availability.…”

Section: The Rangeland Ecology Debatementioning

confidence: 93%

Strategies for global rangeland stewardship: Assessment through the lens of the equilibrium–non‐equilibrium debate

Briske¹,

Coppock

Illius

et al. 2020

Journal of Applied Ecology

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This Review assesses the adequacy of current stewardship strategies to address the accelerating challenges confronting global rangeland systems. The assessment was conducted through the lens of the rangeland ecology debate that was initiated in the late 1980s to determine whether equilibrial or non‐equilibrial models more accurately represented the ecological dynamics of rangeland systems. The following lessons have emerged from this prolonged debate: (a) equilibrial and non‐equilibrial dynamics among plants and herbivores always coexist in individual systems; (b) herbivore persistence is strongly influenced by functional resource heterogeneity; (c) biotic feedbacks are highly dependent upon spatial and temporal scale; (d) multiple stable states separated by nonlinear trajectories may coexist on individual ecological sites and (e) management and policy decisions can have important consequences for rangeland systems despite high environmental stochasticity. These lessons demonstrate that scale and functional heterogeneity were critical ‘blind spots’ within the traditional rangeland profession. In contrast, pastoral strategies recognized these system variables as essential for exploitation of heterogeneous resource distribution, rather than assuming stable, uniform resource distribution. These divergent perceptions of scale and heterogeneity in grazed ecosystems largely explain the disparate interpretations of ecological carrying capacity that was central to the debate. Programmes supporting supplemental feeding and infrastructure development have created an anthropogenic category of non‐equilibrial dynamics by sustaining large numbers of livestock during droughts. These programmes decouple livestock and rangeland resources to create an additional stewardship dilemma regarding complex trade‐offs between livestock production and the capacity of systems to provision a broad array of global ecosystem services. Synthesis and applications. The fundamental challenge facing the global rangeland community may not be identification of a unified model of rangeland ecology—as assumed during the rangeland debate. Rather, the challenge may be how to best transform rangeland social–ecological systems to provide optimal combinations of ecosystem services to meet the needs of global citizens, while improving the well‐being of millions of rangeland residents who are highly dependent upon provisioning services. A comprehensive accounting of rangeland ecosystem services, supported by institutional governance and delivered as state–community partnerships, may provide the foundation for an alternative stewardship strategy to pursue this critical goal.

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“…Previous work has shown the complexities of the factors affecting population processes [35] and, within these, the fundamental role of food acquisition in breeding success has been repeatedly emphasized [36], although the precise mechanistic link between energy gain and population success with respect to food has been unclear.…”

Section: Animal Lifestyle and Ps Valuesmentioning

confidence: 99%

Luck in Food-Finding Affects Individual Performance and Population Trajectories

et al. 2018

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Energy harvesting by animals is important because it provides the power needed for all metabolic processes. Beyond this, efficient food-finding enhances individual fitness [1] and population viability [2], although rates of energy accumulation are affected by the environment and food distribution. Typically, differences between individuals in the rate of food acquisition are attributed to varying competencies [3] even though food encounter rates are known to be probabilistic [4]. We used animal-attached technology to quantify food intake in four disparate free-living vertebrates (condors, cheetahs, penguins and sheep) and found that inter-individual variability depended critically on the probability of food encounter. We modelled this to reveal that animals taking rarer food, such as apex predators and scavengers, are particularly susceptible to breeding failure because this variability results in larger proportions of the population failing to accrue the necessary resources for their young before they starve, and because even small changes in food abundance can affect this variability disproportionately. A test of our model on wild animals indicated why Magellanic penguins have a stable population while the congeneric African penguin population has declined for decades. We suggest that such models predicting probabilistic ruin can help predict the fortunes of species operating under globally changing conditions. RESULTS AND DISCUSSION Consumer resource theory recognizes the importance of food-finding and deals with broad issues ranging from optimal diet models [5] through behavioural strategies [6] to population dynamics and food web structure [7]. However, although some work recognizes the importance of variation in rates of energy accumulation [8] and how animal condition depends on foraging decisions [9], many models ignore such variation and so cannot build appropriate risks of breeding failure or starvation into their outputs. In fact, resources are generally considered to be distributed probabilistically [10], which does not necessarily equate with linear rates of food

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Herbivore population regulation and resource heterogeneity in a stochastic environment

Cited by 37 publications

References 41 publications

Maternal winter body mass and not spring phenology determine annual calf production in an Arctic herbivore

Maternal winter body mass and not spring phenology determine annual calf production in an Arctic herbivore

Strategies for global rangeland stewardship: Assessment through the lens of the equilibrium–non‐equilibrium debate

Luck in Food-Finding Affects Individual Performance and Population Trajectories

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