Climate variability has a stabilizing effect on the coexistence of prairie grasses

Abstract

How expected increases in climate variability will affect species diversity depends on the role of such variability in regulating the coexistence of competing species. Despite theory linking temporal environmental fluctuations with the maintenance of diversity, the importance of climate variability for stabilizing coexistence remains unknown because of a lack of appropriate long-term observations. Here, we analyze three decades of demographic data from a Kansas prairie to demonstrate that interannual climate variability promotes the coexistence of three common grass species. Specifically, we show that (i) the dynamics of the three species satisfy all requirements of ''storage effect'' theory based on recruitment variability with overlapping generations, (ii) climate variables are correlated with interannual variation in species performance, and (iii) temporal variability increases low-density growth rates, buffering these species against competitive exclusion. Given that environmental fluctuations are ubiquitous in natural systems, our results suggest that coexistence based on the storage effect may be underappreciated and could provide an important alternative to recent neutral theories of diversity. Field evidence for positive effects of variability on coexistence also emphasizes the need to consider changes in both climate means and variances when forecasting the effects of global change on species diversity.climate change ͉ competition ͉ grassland ͉ plant community ͉ population dynamics S trong climate variability characterizes ecosystems worldwide, and in many regions this variability is predicted to increase over the next century because of higher frequencies of severe storms and droughts (1, 2). The ecological impacts of increased climate variability are poorly understood (3), especially in comparison with threats posed by increasing mean temperatures (4,5). This gap in empirical research contrasts sharply with a considerable body of theory examining the effects of environmental fluctuations on the maintenance of species diversity (6-9).''Storage effect'' theory derives the conditions under which climate variability will have stabilizing or destabilizing effects on species coexistence (10). The temporal storage effect described in refs. 6 and 9 requires that three conditions be met. To satisfy condition 1, species must have long lifespans to buffer their populations against unfavorable years. For condition 2, species must differ in their response to climate variation. These speciesspecific responses to climate cause each species to experience relatively more intraspecific competition during its favorable years and more interspecific competition during its unfavorable years. Condition 3 requires that the effect of competition on each species must be more severe in years favorable for that species than in unfavorable years. When condition 2 is present, intraspecific competition will be more severe than interspecific competition. As a result, climate variability gives species an advantage when they become ra...

Climate modifies response of non-native and native species richness to nutrient enrichment

“…There are several mechanisms that could explain this difference. For instance, greater annual climate variability could ameliorate the effect of competitive exclusion [23,24] caused by the addition of nutrients [50]. Climatic conditions could also reduce competitive exclusion by modifying the strength of the biotic interactions between native and nonnative species, weakening the negative effect that nutrient enrichment has on the native taxa.…”

“…Precipitation, temperature and water availability are three of the most common variables used to understand how climate shapes species distributions, diversity and trait variation [24,37,41]. Further, these three variables impact on plants' photosynthetic capacity, growth rates and biomass allocation [41,42].…”

“…The effects of eutrophication may be dampened by higher plant diversity and functional composition [22]. Climate variability can contribute to the maintenance of diversity as species vary in their responses to climatic conditions [18,23,24]. In contrast, more constant climate conditions may offer fewer opportunities for temporal niche partitioning [25].…”

“…Over time, species arrival and local environmental conditions will shape the composition of communities [25,35,36], and species characteristics will determine their success in different abiotic environments (including both mean conditions and variability) [24,25,37,38]. However, nutrient addition modifies environmental conditions, changing the composition of communities and reducing species diversity [4,5,8], often causing losses of rare, native, perennial and N-fixing species [8,39].…”

Temporal niche promotes biodiversity during adaptive radiation

“…The theory of temporal niche dynamics (TND) suggests that temporal variation in niche availability allows the storage effect to operate, buffering species against extinction 4,5 . Increased species coexistence in fluctuating environments has been documented for both natural [6][7][8] and experimental 9,10 communities, and has, in a few cases, been explicitly linked to TND 6,11 . In parallel, diversification under fluctuating selection has been of much interest for evolutionary biologists [12][13][14] .…”