Habitat isolation moderates the strength of top‐down control in experimental pond food webs

Abstract

Abstract. Habitat isolation is well known to alter patterns of species' abundance, richness, and the ratios of predators : prey. Less clear, however, is how isolation alters interactions within food webs. Here, we present the results from an experiment performed in artificial ponds (mesocosms) manipulating habitat isolation crossed with a predator reduction treatment to disentangle how isolation mediates the top-down effect of predators. The strength of the trophic cascade, from predators, through herbivores, to producers, was considerably stronger in connected than in isolated habitats. We further found that the overall richness of both predator and herbivore species declined strongly with isolation. Experimental predator reductions suggest that the mechanism underlying the herbivore response was likely mediated by a keystone predator effect; when predators were reduced, herbivore richness was lower, and there was no discernable effect of isolation on herbivore richness. Finally, we found that the composition of predators in more isolated habitats consisted of species that were smaller and likely less effective predators than species that persisted in less isolated habitats. In all, our experiment showed that habitat isolation can alter the structure of communities by a combination of direct effects of the species in question, as well as effects mediated through their interactions in the food web.

Larval dispersal drives trophic structure across Pacific coral reefs

“…1, inset) instead of being positively correlated with, or invariant of total richness as in many terrestrial and aquatic ecosystems 20 . These findings contradict theoretical predictions 13,21 and empirical studies of other ecosystems, which suggest that species highest in the food web should be most sensitive to habitat isolation 4,10,12,22 . Here we develop a mathematical dispersal-colonization-extinction framework that resolves both of these discrepancies.…”

“…2b). The linearized model had the form ln(S) ¼ a 1 þ a 2 d 2 þ a 3 ln(coastal length) þ a 4 6 [i  ln(coastal length)] þ O, where a j are regression coefficients and i is an indicator variable denoting whether each datum was a predator or prey. The statistical fit with Gaussian spatial autocorrelation had the lowest AIC (AIC ¼ 5.2, r 2 ¼ 0.78).…”

“…T op predators are often conspicuously absent from isolated habitats [1][2][3][4][5][6][7][8] . Explanations for such spatial variation in trophic structure are numerous: predators often have greater resource requirements [9][10][11] , larger body sizes 12 , smaller population sizes 13 and slower population growth rates 14 than species lower in the food web.…”

Density-dependent dispersal and relative dispersal affect the stability of predator–prey metacommunities

“…In aquatic predator-prey metacommunities, the mean density of the predator 22 (Didinium nasutum) was highest at intermediate dispersal rates whereas the mean density of 23 the prey (Colpidium striatum) was decreased by dispersal (Holyoak and Lawler 1996b). In 24 trophically more complex metacommunities, dispersal between mesocosms increased 25 predator biomass, decreased herbivore biomass and increased primary producer biomass 26 (Chase et al 2010). This suggests that the trophic cascade was stronger in mesocosms 1 connected by dispersal than in isolated mesocosms.…”

Tyre track pools and puddles – Anthropogenic contributors to aquatic biodiversity

“…Although there has been work in larger man-made water bodies (farm ponds (Céréghino et al 2008;Brainwood and Burgin 2009;Gioria et al 2010), irrigation pools (Abellan et al 2006) experimental ponds used to examine ecological processes and conservation issues (Fairchild et al 1999;Sunahara et al 2002;Blaustein et al 2005;Frisch and Green 2007;Mokany et al 2008;Chase et al 2010;Schröder et al 2012)), studies of small 'accidentally' formed habitats are few. An exception is the work of Bilton et al (2008) who examined the ecology and conservation status of a set of fluctuating and temporary ponds which included some formed on ancient cart tracks, in gateways and along hedgerows.…”