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The native‐exotic species richness relationship varies with spatial grain of measurement and environmental conditions
Author(s) -
Tarasi Dennis D.,
Peet Robert K.
Publication year - 2017
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1002/ecy.2028
Subject(s) - species richness , null model , ecology , spatial ecology , biodiversity , temperate climate , body size and species richness , vegetation (pathology) , scale (ratio) , spatial distribution , temperate forest , introduced species , temperate rainforest , geography , biology , cartography , ecosystem , remote sensing , medicine , pathology
Biological invasions can have dramatic impacts on communities and biodiversity, and are critical considerations in conservation and management decisions. We present a novel analysis to determine how exotic species success varies with community richness and scale of measurement. Using 5,022 plots representing natural vegetation of the Carolinas, we calculated native and exotic species richness of all vascular plants at five grain sizes. To avoid spatial pseudoreplication, we randomly selected unique subplots from each larger plot, re‐selecting 100 times to develop an empirical distribution of the native‐exotic richness relationship ( NERR ). Because observed NERR s vary with spatial scale, we developed separate scale‐specific null‐model distributions to compare to the empirical data. For each spatial scale, we compared the empirical distribution of 100 slopes to the null distribution containing 99 permutations of species origin per empirical slope. We also analyzed the dataset according to broad assignments corresponding to environmental conditions, using the formation type assigned to each community. The plots followed across most scales the general trend that exotic richness increases with native richness. At the smallest scale, however, the NERR was negative. The slope of the NERR is significantly higher than the null model at the largest observed scale and significantly lower than the null model at the smallest two observed scales. The NERR for most formations follows the general pattern with scale for the entire dataset. Warm temperate forests expressed essentially 0 slope at the largest spatial grain, decreasing to a negative relationship at 1 m 2 and smaller. Temperate freshwater marshes and wet meadows and shrublands expressed a positive relationship at all spatial grains, demonstrating that unique environmental and biogeographic conditions differentially affect exotic species. Further, these results indicate that exotic species are unevenly distributed across natural communities and that community assembly processes vary with scale.