Predators and connected habitats (1): isolation weakens top-down control

Posted on March 6, 2011


There are reasons to expect community structure to be influenced by habitat isolation.  In particular, predator species should be affected by isolation more than prey species since the larger body size, higher metabolic needs and smaller population sizes of predators make them more vulnerable to local extinction.  In turn, lower predator abundance and diversity should affect food web dynamics in isolated habitats by reducing the strength of top-down control.  These ideas were tested in a two-year experiment using a series of 1130 – litre plastic tanks containing topsoil, well water and inoculations of algae, macrophytes, plankton and macroinvertebrates.  The tanks were distributed in open fields across an 800 ha research centre inMissouri,U.S.A.  “Isolated” tanks were at least 200m from other tanks, while “connected” tanks were within 5 m of three other tanks.  The experimental predictions were largely supported.  In connected habitats the biomass and diversity of predators were higher, and predators tended to be larger, with more dragonfly larvae and large diving beetles.   The predator-controlled top-down cascade was stronger in connected habitats: the biomass of  herbivores (snails, tadpoles, midge larvae, zooplankton) was depressed while algal biomass was relatively high.

Reference:  Chase, J.M., Burgett, A.A. & Biro, E.G.  2010.  Habitat isolation moderates the strength of top-down control in experimental pond food webs.  Ecology 91(3), 637–643.

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Posted in: ecosystems, food webs