Geographical homogenization but little net change in the local richness of Canadian butterflies

Abstract

Aim: Recent studies have found that local-scale plots measured through time exhibit marked variation in the change in species richness. However, the overall effect often reveals no net change. Most studies to date have been agnostic about the identities of the species lost/gained and about the processes that might lead to these changes.Generalist traits might be crucial in allowing species to colonize new plots or remain resilient in situ, whereas environmental filtering might remove specialists. We test whether plots are changing in species richness, whether they are becoming more similar (i.e., becoming homogenized) through time and whether several generalist traits can predict gains or losses from local plots.Location: Canada.

Regional occupancy increases for widespread species but decreases for narrowly distributed species in metacommunity time series

“…Overall, our results support the hypothesis that small-and largeranged species differ in how they are responding to the last several decades of the Anthropocene. These results generalize previous smaller-scale studies [5][6][7]11,12 to suggest this is a common phenomenon. With our current analyses, however, we cannot directly address the drivers of this result, nor can we specifically determine potential mechanisms behind this overall result for a multitude of taxa, geographic regions, and scales on which the individual studies took place.…”

“…2b). This result is consistent with several smaller-scale regional analyses [5][6][7]11,12 , and may reflect the capacity of large-ranged species to tolerate changing environmental conditions as a result of broader environmental tolerances (e.g., generalist strategies), and/or greater dispersal capacities 8,9 .…”

“…species tend to have wider niche breadth 8 and more frequent dispersal 9 than more narrowly distributed species, and thus are more likely to persist and/or increase in response to global environmental changes. There is some evidence for this hypothesis, for example, when comparing responses of small-and large-ranged species along land-use gradients 10 , and for a few geographically and taxonomically restricted groups through time 5,6,11,12 . However, other studies have failed to find such relationships 13,14 , or even find opposite relationships where narrow-ranged species increased through time 15,16 .…”

Looking back on biodiversity change: lessons for the road ahead

“…However, not all analyses of species richness change find trends centred on zero. For example, species richness increases were found among coastal marine communities [43], temperate marine organisms [44], mountainous plants [45] and Canadian butterflies [46] and invertebrate communities [114]. A review of bird diversity changes found that increases in species richness was the most commonly observed pattern at local scales [47,115].…”

“…[41]) this does not provide direct evidence of homogenization. Among studies of how betadiversity has changed through time, there are consistent signs of homogenization for marine fishes in Scotland [62], freshwater macroinvertebrates in New Zealand [63], Canadian butterflies [46] and birds [47]. Yet, not all studies show homogenization.…”