Topographic determinants of mobile vertebrate predator hotspots: current knowledge and future directions

Abstract

Despite being identified as a driver of mobile predator aggregations (hotspots) in both marine and terrestrial environments, topographic complexity has long remained a challenging concept for scientists to visualise and a difficult parameter to estimate. It is only with the advent of high-speed computers and the recent popularisation of geographical information systems (GIS) that terrain attributes have begun to be quantitatively measured in three-dimensional space and related to wildlife dynamics, making the well-established field of geomorphometry (or 'digital terrain modelling') a discipline of growing appeal to biologists. Although a diverse array of numerical metrics is now available to describe the shape, geometry and physical properties of natural habitats, few of these are known to, or adequately used by, ecologists. In this review, we examine the nature and usage of 56 geomorphometrics extracted from the ecological modelling literature over a period of 32 years (1979-2011). We show that, in studies of mobile predators, numerous topographic variables have largely been overlooked in favour of single basic metrics that do not, on their own, fully capture the complexity of continuous landscapes. Based on a simulation approach, we assess the redundancy and correlation structure of these metrics and demonstrate that a majority are highly collinear. We highlight a suite of 7-8 complementary metrics which best explain topographic patterns across a bathymetric grid of the west Australian seafloor, and contend that field and analytical protocols should prioritise variables of these types, particularly when the responses of predator populations to physical habitat features are of interest. We suggest that prominent structures such as canyons, seamounts or mountain chains can serve as useful proxies for predator hotspots, especially in remote locations where access to high-resolution biological data is often limited.

Comparing Selections of Environmental Variables for Ecological Studies: A Focus on Terrain Attributes

“…Many different terrain attribute selections have been used in terrestrial and marine ecology ([1,7]; references therein). In a meta-analysis of ecological studies using geomorphometry, Bouchet et al .…”

“…In a meta-analysis of ecological studies using geomorphometry, Bouchet et al . [1] found that about a third of the studies only used one terrain attribute and that very few authors used more than four. While focusing on forest ecosystems, Sharaya & Sharyi [40] wrote that in general, one to three basic terrain attributes are used to study landscape phenomena and that the “insufficient representativeness” ( ibid , p. 2) of terrain attributes makes for an inefficient use of topography as a variable in ecology.…”

“…g . slope, rugosity, aspect) derived from digital elevation (DEM) or bathymetric (DBM) models have proven their value in a broad range of terrestrial and marine ecological studies [1]. Such attributes can now be derived easily using tools available in most Geographic Information Systems (GIS).…”

Combined influence of meso-scale circulation and bathymetry on the foraging behaviour of a diving predator, the king penguin (Aptenodytes patagonicus)

“…However, topographically complex landscapes such as the shelf break and areas near the Chun Spur may lead to spatially localized and stable micro-niches in terms of oceanography and associated prey resources (Bouchet et al, 2014). Such conditions may allow for shorter search times for prey patches, and therefore increase foraging profitability in terms of CPUE on the foraging trip scale.…”

Multiscale and Hierarchical Classification for Benthic Habitat Mapping

“…Collecting biological data over broad spatial scales is often time consuming and expensive, resulting in the use of abiotic surrogates, such as terrain attributes, to associate with habitat classes for extrapolation [12,23]. Bathymetry and backscatter are the primary products of acoustic sampling providing full coverage data of the seafloor.…”