Climate-induced temporal variation in the productivity-diversity relationship.
Laughlin, Daniel*,1, Moore, Margaret1, 1 Northern Arizona University, Flagstaff, AZ
ABSTRACT- The relationship between productivity and diversity has recently been shown to be significantly affected by the spatial scale of measurement. However, less attention has been given to the importance of temporal scale when examining this relationship. We hypothesized that climate-induced temporal variation in understory production could fundamentally change the relationship between productivity and diversity, which often exhibit nonlinear relations. Inter-annual climatic variation in semi-arid pine forests causes dramatic year-to-year differences in understory plant production. We hypothesized that a unimodal (or hump-backed) relationship would be detected in wet years, whereas a positive monotonic or asymptotic relationship would be detected in drought years since less production would decrease the likelihood of competitive interactions. We analyzed 14 years of maximum total standing crop and total species richness data using structural equation modeling. Herbaceous standing crop exhibited a unimodal relationship to species richness in wet years (R2>0.70), suggesting that density effects, such as competitive exclusion, occurred within the understory community in years of high production. However, standing crop exhibited asymptotic relations, rather than unimodal relations, with richness in drought years (R2>0.60), suggesting that competitive exclusion can occur only in years when enough moisture is available to drive abundant plant growth. Across all years, standing crop was suppressed by the density of highly competitive ponderosa pine trees (R2>0.49), which reduce soil moisture, nutrient availability, and light. These results suggest that climatic variation can affect species interactions in semi-arid plant communities and that climate-induced changes to the productivity-diversity relationship can change the interpretation of diversity models from year-to-year.
Key words: competitive exclusion, community ecology, ponderosa pine forest
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