The role of drought- and disturbance-mediated competition in shaping community responses to varied environments

Abstract

By altering the strength of intra- and interspecific competition, droughts may reshape plant communities. Furthermore, species may respond differently to drought when other influences, such as herbivory, are considered. To explore this relationship, we conducted a greenhouse experiment measuring responses to inter- and intraspecific competition for two grasses, Schedonorus arundinaceus and Paspalum dilatatum, while varying water availability and simulating herbivory via clipping. We then parameterized population growth models to examine the long-term outcome of competition under these conditions. Under drought, S. arundinaceus was less water stressed than P. dilatatum, which exhibited severe water stress; clipping alleviated this stress, increasing the competitive ability of P. dilatatum relative to S. arundinaceus. Although P. dilatatum competed weakly under drought, clipping reduced water stress in P. dilatatum, thereby enhancing its ability to compete with S. arundinaceus under drought. Supporting these observations, population growth models predicted that P. dilatatum would exclude S. arundinaceus when clipped under drought, while S. arundinaceus would exclude P. dilatatum when unclipped under drought. When the modeled environment varied temporally, environmental variation promoted niche differences that, though insufficient to maintain stable coexistence, prevented unconditional competitive exclusion by promoting priority effects. Our results suggest that it is important to consider how species respond not just to stable, but also to variable, environments. When species differ in their responses to drought, competition, and simulated herbivory, stable environments may promote competitive exclusion, while fluctuating environments may promote coexistence. These interactions are critical to understanding how species will respond to global change.

Abiotic heterogeneity underlies trait‐based competition and assembly

“…As a result, we can better understand the processes shaping invader success and ultimately the patterns of diversity by considering the simultaneous effects of many factors on the key demographic rates of species (i.e., fitness landscapes). The interaction we found between the environment and functional diversity not only supports findings from simpler, low‐diversity experiments (Hart & Marshall, ; Loughnan & Gilbert, ; Napier et al, ), it emphasizes the need for joint and simultaneous consideration of biotic and abiotic drivers of community assembly.…”

“…In our study, communities with high functional diversity conferred low invasion success, but this effect was more pronounced when abiotic conditions were harsh (low macronutrient availability and low soil moisture). This result contradicts many classic models that posit that competition is reduced in stressful environments, but is consistent with recent theory and experiments (e.g., Hart & Marshall, ; Napier, Mordecai, & Heckman, ). Intuitively, although species may be able to survive harsh environmental conditions or high competition, the combination of these stressors can lead to disproportionately high mortality.…”

Drought weakens the positive effects of defoliation on native rhizomatous grasses but enhances the drought‐tolerance traits of native caespitose grasses

“…Drought has been reported to intensify the responses of plant species to defoliation (Chen et al., ; Heitschmidt, Klement, & Haferkamp, ). Meanwhile, defoliation also may weaken the negative impact of drought stress through reducing the importance of water availability (Napier, Mordecai, & Heckman, ). Our results showed that clipping led to a drastic decline in the R/S ratio of the native grasses, which may be an important emergency mechanism of native plants to damage by allocating the photosynthesis carbon from root system to new shoots and leaves of compensatory growth (Mokany, Raison, & Prokushkin, ; Zhao, Chen, & Lin, ).…”

Increased Vegetation Greenness Aggravates Water Conflicts during Lasting and Intensifying Drought in the Poyang Lake Watershed, China

“…Especially in the core areas of the afforestation and reforestation projects, an increase of 20-80% in vegetation could lead to a reduction of 9-27% in water yield under lasting and intensifying drought conditions. The reason was that tree species have high water use efficiency but low maximal rates of photosynthesis for maintaining growth under these drought conditions, leading to water consumption and thereby water yield reduction [54,55].…”