Dispersal Rates Affect Species Composition in Metacommunities ofSarracenia purpureaInquilines

Abstract

Dispersal among local communities can have a variety of effects on species composition and diversity at local and regional scales. Local conditions (e.g., resource and predator densities) can have independent effects, as well as interact with dispersal, to alter these patterns. Based on metacommunity models, we predicted that local diversity would show a unimodal relationship with dispersal frequency. We manipulated dispersal frequencies, resource levels, and the presence of predators (mosquito larvae) among communities found in the water-filled leaves of the pitcher plant Sarracenia purpurea. Diversity and abundance of species of the middle trophic level, protozoa and rotifers, were measured. Increased dispersal frequencies significantly increased regional species richness and protozoan abundance while decreasing the variance among local communities. Dispersal frequency interacted with predation at the local community scale to produce patterns of diversity consistent with the model. When predators were absent, we found a unimodal relationship between dispersal frequency and diversity, and when predators were present, there was a flat relationship. Intermediate dispersal frequencies maintained some species in the inquiline communities by offsetting extinction rates. Local community composition and the degree of connectivity between communities are both important for understanding species diversity patterns at local and regional scales.

Are natural microcosms useful model systems for ecology?

“…between patches of moss [17,18]) or by experimental additions (e.g. rotifers and protozoa pipetted between pitcher plants [22] or seeds added to riverine tussocks [12]). Researchers have laid out groups of marine pen shells [23,24] and fungal-sporocarps [25,26] in different patterns to examine the effects of spatial structure (e.g.…”

“…At low dispersal rates, dominant competitors exclude other species, whereas, at high dispersal rates, the species with low dispersal abilities are unable to persist regionally, reducing local richness. The first test of this model was carried out in pitcher plants, and involved manipulating the dispersal rate of microorganisms by pipetting specific water volumes between pitchers [22]. Local diversity was highest at intermediate dispersal rates, as predicted by the model, but this pattern disappeared in the presence of predators [22].…”

“…The first test of this model was carried out in pitcher plants, and involved manipulating the dispersal rate of microorganisms by pipetting specific water volumes between pitchers [22]. Local diversity was highest at intermediate dispersal rates, as predicted by the model, but this pattern disappeared in the presence of predators [22]. A related model [23] predicts that the strongest correlation between local and regional richness will occur at intermediate assembly times.…”

“…At the local (pitcher) scale, species diversity of many microscopic organisms (bacteria, rotifers and protozoa) is strongly affected by both TOP-DOWN (mosquito occurrence) and BOTTOM-UP (carcass provisioning) processes [7,9,13,22,46]. Mosquito occurrence at the pitcher scale is affected by bottom-up effects, such as carcass provisioning [43], carcass processing by midges [47] and pitcher size [43,48].…”

Metapopulation Extinction Thresholds in Rain Forest Remnants

“…By extension, this hypothesis predicts that habitat destruction will result in declines in both a species' local abundance and site occupancy as a result of lower per-patch colonization rates (Harrison 1991;Gonzalez et al 1998). However, previous studies of the rescue effect dynamic in the context of habitat fragmentation have been mostly limited to controlled laboratory (Burkey 1997) or mesocosm (Gonzalez et al 1998;Kneitel and Miller 2003;Rantalainen et al 2004) experiments (but see Davies et al 2001 for an example at the landscape scale).…”