Animal movement in the absence of predation: environmental drivers of movement strategies in a partial migration system

Bastille‐Rousseau, Guillaume; Gibbs, James P.; Yackulic, Charles B.; Frair, Jacqueline L.; Cabrera, Fredy; Rousseau, Louis-Philippe; Wikelski, Martin; Kümmeth, Franz; Blake, Stephen

doi:10.1111/oik.03928

Cited by 38 publications

(39 citation statements)

References 59 publications

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“…This was particularly evident with giant tortoises where clear patterns of partial migration have been documented previously using net squared displacement (Bastille‐Rousseau et al. ), yet very few individuals were found in the PCA space associated with migratory or resident individuals (Fig. ).…”

Section: Discussionsupporting

confidence: 64%

Applying network theory to animal movements to identify properties of landscape space use

Bastille‐Rousseau

Douglas‐Hamilton

Blake

et al. 2018

Ecological Applications

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Network (graph) theory is a popular analytical framework to characterize the structure and dynamics among discrete objects and is particularly effective at identifying critical hubs and patterns of connectivity. The identification of such attributes is a fundamental objective of animal movement research, yet network theory has rarely been applied directly to animal relocation data. We develop an approach that allows the analysis of movement data using network theory by defining occupied pixels as nodes and connection among these pixels as edges. We first quantify node-level (local) metrics and graph-level (system) metrics on simulated movement trajectories to assess the ability of these metrics to pull out known properties in movement paths. We then apply our framework to empirical data from African elephants (Loxodonta africana), giant Galapagos tortoises (Chelonoidis spp.), and mule deer (Odocoileous hemionus). Our results indicate that certain node-level metrics, namely degree, weight, and betweenness, perform well in capturing local patterns of space use, such as the definition of core areas and paths used for inter-patch movement. These metrics were generally applicable across data sets, indicating their robustness to assumptions structuring analysis or strategies of movement. Other metrics capture local patterns effectively, but were sensitive to specified graph properties, indicating case specific applications. Our analysis indicates that graph-level metrics are unlikely to outperform other approaches for the categorization of general movement strategies (central place foraging, migration, nomadism). By identifying critical nodes, our approach provides a robust quantitative framework to identify local properties of space use that can be used to evaluate the effect of the loss of specific nodes on range wide connectivity. Our network approach is intuitive, and can be implemented across imperfectly sampled or large-scale data sets efficiently, providing a framework for conservationists to analyze movement data. Functions created for the analyses are available within the R package moveNT.

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Section: Discussionsupporting

confidence: 64%

Applying network theory to animal movements to identify properties of landscape space use

Bastille‐Rousseau

Douglas‐Hamilton

Blake

et al. 2018

Ecological Applications

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“…, Bastille‐Rousseau et al. ). We build on a sample of known migratory individuals from three different species, with most individuals now followed continuously for >5 yr (Bastille‐Rousseau et al.…”

Section: Introductionmentioning

confidence: 99%

“…We build on a sample of known migratory individuals from three different species, with most individuals now followed continuously for >5 yr (Bastille‐Rousseau et al. ). Migration in giant tortoises is influenced by spatiotemporal gradients in forage productivity and temperature and their interactions with body size (Bastille‐Rousseau et al.…”

Section: Introductionmentioning

confidence: 99%

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Migration triggers in a large herbivore: Galápagos giant tortoises navigating resource gradients on volcanoes

Bastille‐Rousseau

Yackulic

Gibbs

et al. 2019

Ecology

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To understand how migratory behavior evolved and to predict how migratory species will respond to global environmental change it is important to quantify the fitness consequences of intra‐ and inter‐individual variation in migratory behavior. Intra‐individual variation includes behavioral responses to changing environmental conditions and hence behavioral plasticity in the context of novel or variable conditions. Inter‐individual variation determines the degree of variation on which selection can act and the rate of evolutionary responses to changes in average and extreme environmental conditions. Here we focus on variation in the partial migratory behavior of giant Galápagos tortoises (Chelonoidis spp.) and its energetic consequences. We evaluate the extent and mechanisms by which tortoises adjust migration timing in response to varying annual environmental conditions, and integrate movement data within a bioenergetic model of tortoise migration to quantify the fitness consequences of migration timing. We find strong inter‐individual variation in the timing of migration, which was not affected by environmental conditions prevailing at the time of migration but rather by average expectations estimated from multi‐annual averaged conditions. This variation is associated with an average annual loss in efficiency of ~15% relative to optimal timing based on year‐specific conditions. These results point towards a limited ability of tortoises to adjust the timing of their migrations based on prevailing (and, by extension, future) conditions, suggesting that the adaptability of tortoise migratory behavior to changing conditions is predicated more by past “normal” conditions than responses to prevailing, changing conditions. Our work offers insights into the level of environmental‐tuning in migratory behavior and a general framework for future research across taxa.

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“…Studies across disparate species and ecosystems demonstrate support for the forage maturation hypothesis (Bastille-Rousseau et al, 2017;Hebblewhite, Merrill, & McDermid, 2008), which posits that herbivores migrate to increase access to high-quality forage where vegetative conditions vary spatially and temporally (Fryxell, 1991). Studies across disparate species and ecosystems demonstrate support for the forage maturation hypothesis (Bastille-Rousseau et al, 2017;Hebblewhite, Merrill, & McDermid, 2008), which posits that herbivores migrate to increase access to high-quality forage where vegetative conditions vary spatially and temporally (Fryxell, 1991).…”

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confidence: 95%

Native forage mediates influence of irrigated agriculture on migratory behaviour of elk

Barker

Mitchell

Proffitt

2019

Journal of Animal Ecology

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Ungulates migrate to maximize nutritional intake when forage varies seasonally. Populations of ungulates often include both migratory and non‐migratory individuals, but the mechanisms driving individual differences in migratory behaviour are not well‐understood. We quantified associations between hypothesized drivers of partial migration and the likelihood of migration for individual ungulates that experienced a range of environmental conditions and anthropogenic influences. We evaluated the effects of forage variation, conspecific density, and human land uses on migratory behaviour of 308 adult female elk in 16 herds across western Montana. We found irrigated agriculture on an individual's winter range reduced migratory behaviour, but individuals were more likely to migrate away from irrigated agricultural areas if better forage was available elsewhere or if they experienced high conspecific density on their winter range. When the forage available during the summer growing season varied predictably between years, elk were more likely to migrate regardless of whether they had access to irrigated agriculture. Our study shows that predictable availability of beneficial native forage can encourage migration even for ungulates with irrigated agriculture on their winter range. Perturbations that can affect the forage available to ungulates include wildfires, timber harvest, livestock grazing and changing weather patterns. If these or other disturbances negatively affect forage on summer ranges of migrants, or if they cause forage to vary unpredictably across space and time, our results suggest migratory behaviour may decline as a result.

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Animal movement in the absence of predation: environmental drivers of movement strategies in a partial migration system

Cited by 38 publications

References 59 publications

Applying network theory to animal movements to identify properties of landscape space use

Applying network theory to animal movements to identify properties of landscape space use

Migration triggers in a large herbivore: Galápagos giant tortoises navigating resource gradients on volcanoes

Native forage mediates influence of irrigated agriculture on migratory behaviour of elk

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