2020 ESA Annual Meeting (August 3 - 6)

COS 248 Abstract - Coexistence of alpine and lowland plants across an elevational climate gradient

Shengman Lyu and Jake Alexander, Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland
Background/Question/Methods

Climate change can affect plant species’ distribution and community structure both directly by affecting species’ performance, and indirectly by altering the way in which they interact (e.g. altering competitive ability and niche overlap). The direct effects have been well studied. However, given the complex experiments needed to quantify competitive ability and niche differences, detailed studies of changing interactions and underlying mechanisms in different environmental conditions remain scarce. In this study, we conducted a competition experiment using 7 lowland and 7 alpine plants at three sites across an elevational gradient (830 m, 1400 m, and 1900 m a.s.l.) in the western Swiss Alps. With a response-surface design, we parameterized Beverton-Holt competition models which describe the negative effect of neighbor density on focal plant growth and enable us to estimate specie’s intrinsic growth rate, (i.e. focal plants’ growth in the absence of neighbors) and competition coefficients, (i.e. per capita competitive effects of neighbors). Further, we quantified niche differences, fitness differences and competitive outcomes between pairs of plant species. With this experiment, we ask (1) how changing climate affects the outcome of interactions, and (2) to what extent these changes are driven by differences in performance, competitive ability and niche overlap between species.

Results/Conclusions

We found that among all 74 species pairs across three sites (20 pairs in low and medium sites and 34 pairs in the high site), 31 pairs were predicted to stably coexist, while interactions led to competitive exclusion in 36 pairs and priority effects in 7 pairs. Our results also show that with warming climate, simulated by decreasing elevation, competitive outcomes of 29 species pairs remain qualitatively unchanged (totally 44 pairs can be compared from colder to warmer sites) while for 12 pairs we observed a switch in competitive dominance. We also found that warming climate promoted species coexistence in 9 species pairs, with shifts from predictions of competitive exclusion in colder climates to coexistence in warmer climates. In only 6 species pairs did warming lead to competitive exclusion. Interestingly, our models predicted that warming climate promoted species coexistence by differentiating fitness differences and diminishing niche overlap simultaneously. In contrast, shifts from coexistence to competition resulted exclusively from increasing fitness differences. Taken together, these results indicate the complex effects that climate can have on species’ interactions and underscores the challenges of predicting the response of plant population and community to climate change.