Suite of simple metrics reveals common movement syndromes across vertebrate taxa

Abrahms, Briana; Seidel, Dana Paige; Dougherty, Eric R.; Hazen, Elliott L.; Bograd, Steven J.; Wilson, Alan M.; McNutt, J. Weldon; Costa, Daniel P.; Blake, Stephen; Brashares, Justin S.; Getz, Wayne M.

doi:10.1186/s40462-017-0104-2

Cited by 80 publications

(146 citation statements)

References 72 publications

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“…Some species have intrinsic variability in their movement patterns at individual and population scales, which can make observing clear responses to changing conditions more difficult (Abrahms et al . ). Moreover, the same benefits that top predators convey in integrating ecosystem processes may mean they exhibit a delayed response compared with other ecosystem components.…”

Section: What Makes a Good Sentinel Species?mentioning

confidence: 97%

Marine top predators as climate and ecosystem sentinels

Hazen

Abrahms

Brodie

et al. 2019

Frontiers in Ecol & Environ

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272

157

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The rapid pace of environmental change in the Anthropocene necessitates the development of a new suite of tools for measuring ecosystem dynamics. Sentinel species can provide insight into ecosystem function, identify hidden risks to human health, and predict future change. As sentinels, marine apex (top) predators offer a unique perspective into ocean processes, given that they can move across ocean basins and amplify trophic information across multiple spatiotemporal scales. Because use of the terms “ecosystem sentinel” and “climate sentinel” has proliferated in the scientific literature, there is a need to identify the properties that make marine predators effective sentinels. We provide a clear definition of the term “sentinel”, review the attributes of species identified as sentinels, and describe how a suite of such sentinels could strengthen our understanding and management of marine ecosystems. We contend that the use of marine predators as ecosystem sentinels will enable rapid response and adaptation to ecosystem variability and change.

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Section: What Makes a Good Sentinel Species?mentioning

confidence: 97%

Marine top predators as climate and ecosystem sentinels

Hazen

Abrahms

Brodie

et al. 2019

Frontiers in Ecol & Environ

Self Cite

272

157

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show abstract

“…, Abrahms et al. ). Betweenness performed relatively poorly in classifying simulated core areas, but was more effective at identifying interpatch movements and appeared to work well in identifying key connectivity passages on empirical data sets.…”

Section: Discussionmentioning

confidence: 99%

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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“…To demonstrate how this approach may be applied to typical GPS‐based relocation data, we obtained the dataset reported by Abrahms et al. (). This dataset includes relocation data at a consistent 1‐hr fix rate for multiple species and individuals within species.…”

Section: Methodsmentioning

confidence: 99%

Net displacement and temporal scaling: Model fitting, interpretation and implementation

2018

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Net displacement is an integral component of numerous ecological processes and is critically dependent on the tortuosity of a movement trajectory and hence on the temporal scale of observation. Numerous attempts have been made to quantitatively describe net displacement while accommodating tortuosity, typically evoking a power law, but scale‐dependency in tortuosity limits the utility of approaches based on power law relationships that must assume scale‐invariant tortuosity. We describe a phenomenological model of net displacement that permits both scale‐variant and scale‐invariant movement. Movement trajectories are divided into pairs of relocations specifying start‐ and end‐points, and net displacements between points are calculated across a vector of time intervals. A bootstrap is implemented to create new datasets that are independent both across and within time intervals, and the model is fitted to the bootstrapped dataset using log–log regression. We apply this model to simulated trajectories and both fine‐grain and coarse‐grain trajectories obtained from an Aldabra giant tortoise Aldabrachelys gigantea, African elephants Loxodonta africana, black‐backed jackals Canis mesomelas and Northern elephant seals Mirounga angustirostris. The model was able to quantify the characteristics of net displacement from simulated movement trajectories corresponding to both scale‐variant (e.g. correlated random walks) and scale‐invariant (e.g. random walk) movement models. Furthermore, the model produced identical outputs across time vectors corresponding to different intervals and absolute ranges of time for scale‐invariant models. The model characterized the tortoise as generally exhibiting long scale‐invariant steps, which was corroborated by visual comparison of model outputs to observed trajectories. Elephants, jackals and seals exhibited movement parameters consistent with their known movement behaviours (nomadism, territoriality and widely ranging searching). We describe how the model may be used to compare movements within and between species, for example by partitioning movement into scale‐variant and scale‐invariant components, and by calculating a unitless net displacement scaled to the basal movement capacities of an animal. We also identify several useful derived quantities and realistic parameter ranges and discuss how the model may be implemented in a variety of ecological studies.

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Suite of simple metrics reveals common movement syndromes across vertebrate taxa

Cited by 80 publications

References 72 publications

Marine top predators as climate and ecosystem sentinels

Marine top predators as climate and ecosystem sentinels

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

Net displacement and temporal scaling: Model fitting, interpretation and implementation

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