Investigating the community consequences of competition among clonal plants

Abstract

Although clonal plants comprise most of the biomass of several widespread ecosystems, including many grasslands, wetlands, and tundra, our understanding of the effects of clonal attributes on community patterns and processes is weak. Here we present the conceptual basis for experiments focused on manipulating clonal attributes in a community context to determine how clonal characteristics affect interactions among plants at both the individual and community levels. All treatments are replicated at low and high density in a community density series to compare plant responses in environments of different competitive intensity. We examine clonal integration, the sharing of resources among ramets, by severing ramets from one another and comparing their response to ramets with intact connections. Ramet aggregation, the spacing of ramets relative to each other, is investigated by comparing species that differ in their natural aggregation (either clumped growth forms, with ramets tightly packed together, or runner growth forms, with ramets loosely spread) and by planting individual ramets of all species evenly spaced throughout a mesocosm. We illustrate how to test predictions to examine the influence of these two clonal traits on competitive interactions at the individual and community levels. To evaluate the effect of clonal integration on competition, we test two predictions: at the individual level, species with greater clonal integration will be better individual-level competitors, and at the community level, competition will cause a greater change in community composition when ramets are integrated (connected) than when they are not. For aggregation we test at the individual level: clumped growth forms are better competitors than runner growth forms because of their ability to resist invasion, and at the community level: competition will have a greater effect on community structure when ramets are evenly planted. An additional prediction connects the individual-and community-level effects of competition: resistance ability better predicts the effects of competition on relative abundance in a community than does invasion ability. We discuss additional experimental design considerations as revealed by our ongoing studies. Examining how clonal attributes affect both the individual-and community-level effects of competition requires new methods and metrics such as those presented here, and is vital to understanding the role of clonality in community structure of many ecosystems.

Testing Fox's assembly rule: does plant invasion depend on recipient community structure?

“…This is an early attempt at identifying functional groups for forest communities. Other functional classifications such as different clonal growth forms (Gough et al 2001), canopy stratification (Wilson 1989b), shade tolerance (Hubbell and Foster 1986), woody vs herbaceous plants (Reich et al 2003), pollination mode (Faegri and van der Pijl 1979), or rooting depths might have yielded very different results. Additionally, our view of resource gathering may be quite different from that of an autotrophic organism (Simberloff and Dayan 1991).…”

Architectural and growth traits differ in effects on performance of clonal plants: an analysis using a field‐parameterized simulation model

“…We further compared three variables that capture specific components of performance: mean size of produced ramets, number of ramets and total length of spacers, as a measure of colonization ability. Differential investment into these components can dramatically change competitive ability of clonal plants (Gough et al 2001). In this way we can address whether varying a single trait produces uniform responses in all three performance components, or, alternatively, has qualitatively different effects on each of the components, which could result in tradeoffs among performance components.…”

Effects of Heterogeneous Competitor Distribution and Ramet Aggregation on the Growth and Size Structure of a Clonal Plant

“…Therefore, we hypothesize that, when confronted with interspecific competitors, clonal plants grow better and show less size variation when offspring ramets are aggregated than when they are segregated. To our knowledge, however, few studies have explicitly tested the effect of intraspecific aggregation of offspring ramets on the growth and size structure of clonal plant populations [36], [37], especially in environments with a patchy distribution of competitors.…”