Surprises on habitat structure

Posted on July 2, 2014

Habitat structure is thought to have a crucial influence on the composition, diversity and abundance of animal communities. Complex and varied freshwater habitats are generally thought to increase macroinvertebrate diversity and abundance by providing more ecological niches, increasing food and refuge availability, and easing competitive pressures. However, the evidence in support of these ideas is equivocal, partly because habitat complexity and heterogeneity are hard to measure and often poorly defined. Researchers at Cardiff University, U.K. sampled habitats and macroinvertebrates at the patch scale (<0.1 m2) at different sites in the rivers Wye and Usk. They defined habitat heterogeneity in terms of the composition and configuration of different habitat types (bedrock, silt, sand, gravel, pebbles, cobbles), and expressed habitat complexity as the total abundance of structural features (e.g. surface crevices) in a given area. They used a range of multivariate methods to analyse their data. Somewhat surprisingly, they found that macroinvertebrate diversity and abundance weren’t influenced by habitat heterogeneity, and were only weakly affected by habitat complexity when the confounding effect of surface area was factored out. Much more variation in the data was explained by habitat type. This means that river macroinvertebrate communities may be influenced less by habitat structure than by other factors, such as surface porosity, hydraulic conditions and local resource distributions.

Reference: Barnes, J.B., Vaughan, I.P. & Ormerod, S.J. 2013. Reappraising the effects of habitat structure on river macroinvertebrates Freshwater Biology 58, 2154–2167.