Abstract
Darwin's naturalization conundrum describes the paradigm that community assembly is regulated by two opposing processes, environmental filtering and competitive interactions, which predict both similarity and distinctiveness of species to be important for establishment. Our goal is to use long‐term, large‐scale, and high‐resolution temporal data to examine diversity patterns over time and assess whether environmental filtering or competition plays a larger role in regulating community assembly processes. We evaluated Darwin's naturalization conundrum and how functional diversity has changed in the Laurentian Great Lakes fish community from 1870 to 2010, which has experienced frequent introductions of non‐native species and extirpations of native species. We analyzed how functional diversity has changed over time by decade from 1870 to 2010 at three spatial scales (regional, lake, and habitat) to account for potential noninteractions between species at the regional and lake level. We also determined which process, environmental filtering or competitive interactions, is more important in regulating community assembly and maintenance by comparing observed patterns to what we would expect in the absence of an ecological mechanism. With the exception of one community, all analyses show that functional diversity and species richness has increased over time and that environmental filtering regulates community assembly at the regional level. When examining functional diversity at the lake and habitat level, the regulating processes become more context dependent. This study is the first to examine diversity patterns and Darwin's conundrum by integrating long‐term, large‐scale, and high‐resolution temporal data at multiple spatial scales. Our results confirm that Darwin's conundrum is highly context dependent.
Highlights
Human-assisted movement has broken down natural barriers to the dispersal of species, drastically increasing both the rate and spatial scale at which biotic exchange occurs (Hulme, 2009; Olden, Poff, Douglas, Douglas, & Fausch, 2004)
We have found increases in species richness and functional diversity in the Laurentian Great Lakes, the majority of studies show that non-n ative species pose a large threat to native community biodiversity (Powell, Chase, & Knight, 2013; Sala et al, 2000; Vilà et al, 2011)
Our results have shown that the addition of non-native species in the Great Lakes has increased functional diversity, at both regional and lake levels over the past 140 years and appears to be primarily regulated by environmental filtering at a regional spatial scale; the ability to evaluate Darwin’s conundrum is dependent on the spatial scale at which a study is completed
Summary
Human-assisted movement has broken down natural barriers to the dispersal of species, drastically increasing both the rate and spatial scale at which biotic exchange occurs (Hulme, 2009; Olden, Poff, Douglas, Douglas, & Fausch, 2004). We have high temporal replicates and examine patterns of diversity at multiple spatial scales to understand and identify how diversity is changing through time and what is driving the patterns, which allows us to evaluate Darwin’s naturalization conundrum using the Laurentian Great Lakes as a study system. We expect that our ability to interpret Darwin’s conundrum will be more informative at smaller spatial scales where species are interacting (i.e., at the habitat level) and that, through identifying the most appropriate temporal scale, we will gain high temporal resolution, which will provide the first evidence of long-term diversity dynamics with the ability to understand how diversity changes in short time-steps in response to the addition of non-native species and extirpation of native species. This study is the first to comprehensively integrate long-term, large-scale, and high- resolution temporal data and multiple spatial scales to analyze diversity patterns over time and to evaluate Darwin’s conundrum
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