Dispersal and diversity in experimental metacommunities: linking theory and practice

Abstract

There has been a recent rise in the number of experiments investigating the effect of dispersal on diversity, with many of the predictions for these tests derived from metacommunity theory. Despite the promise of linking observed relationships between dispersal and diversity to underlying metacommunity processes, empirical studies have faced challenges in providing robust tests of theory. We review experimental studies that have tested how dispersal affects metacommunity diversity to determine why shortcomings emerge, and to provide a framework for empirical tests of theory that capture the processes structuring diversity in natural metacommunities. We first summarize recent experimental work to outline trends in results and to highlight common methods that cause a misalignment between empirical studies and the processes described by theory. We then identify the undesired implications of three widely used experimental methods that homogenize metacommunity structure or species traits, and present alternative methods that have been used to successfully integrate experiments and theory in a biologically relevant way. Finally, we present methodological and theoretical insights from three related ecological fields (coexistence, food web and priority effects theory) that, if integrated into metacommunity experiments, could help isolate the independent and joint effects of local interactions and dispersal on diversity, and reveal the mechanisms underlying observed dispersal–diversity patterns. Together, these methods can provide stronger tests of existing theory and stimulate new theoretical explorations.

Experimental dispersal reveals characteristic scales of biodiversity in a natural landscape

“…A presence/absence matrix was created from percentage of cover estimates of all 73 annual species in 29 of the 30 sites that were sampled; data from one site were lost due to a corrupt data file. We used presence/absence data because it is most appropriate for tracking gains and losses of species in response to manipulations of species pools and is most comparable to other studies (14,29). We tested the responses of five components of diversity to our species pool manipulations: net changes in species richness, species richness, regional site occupancy, species composition (PCoA axis 1 and 2 scores), and beta diversity.…”

“…S1D; no change in species richness) (8,16). In the metacommunity ecology literature, these four potential outcomes of increasing dispersal would correspond to species sorting, mass effects, and neutral dynamics (with or without dispersal limitation), respectively (9,16 (14,15,22), but has yet to be implemented in the field with natural spatial structure in species pools, abundance distributions, and environments.…”

“…Manipulative tests of local and regional diversity are typically performed in mesocosm experiments on communities constructed using simplified environments, species pools, or dispersal patterns (14). Because it is often unclear how such simplifications affect experimental outcomes (15), mesocosm experiments allow essential tests of the range of potential outcomes under different sets of experimental conditions, but cannot capture the importance of processes that occur in nature.…”

The legacy of the past: effects of historical processes on microbial metacommunities

“…Moreover, the likelihood of priority effects increases due to the lower number of potential colonizers/competitors arriving via dispersal (e.g. Fukami 2015, Vanoverbeke et al 2015, Grainger & Gilbert 2016). How dispersal rates affect the occurrence of priority effects has rarely been tested, with the exception of one recent study that did not provide support for the theoretical prediction that higher dispersal should weaken the importance of priority effects because the likelihood for the arrival of better-adapted dispersing species increases (Pu & Jiang 2015).…”

“…Most importantly, legacy effects will primarily be influenced by the adaptive potential and growth rates of local communities in relation to the time it takes for better adapted external taxa and/or dormant resident taxa to arrive or resuscitate and grow to become abundant community members. This will then ultimately determine the relative importance of contemporary species sorting processes compared to historical processes (Urban & De Meester 2009, Mergeay et al 2011, Fukami 2015, Vanoverbeke et al 2015, Grainger & Gilbert 2016. If dispersal rates are high and dispersed taxa that are selected by the new environmental conditions grow rapidly, the time window for which the legacy of past environmental conditions can be detected should be short (Fig.…”