Abstract
In contrast to secondary succession, studies of terrestrial primary succession largely ignore the role of biotic interactions, other than plant facilitation and competition, despite the expectation that simplified interaction webs and propagule-dependent demographics may amplify the effects of consumers and mutualists. We investigated whether successional context determined the impact of consumers and mutualists by quantifying their effects on reproduction by the shrub Vaccinium membranaceum in primary and secondary successional sites at Mount St. Helens (Washington, USA), and used simulations to explore the effects of these interactions on colonization. Species interactions differed substantially between sites, and the combined effect of consumers and mutualists was much more strongly negative for primary successional plants. Because greater local control of propagule pressure is expected to increase successional rates, we evaluated the role of dispersal in the context of these interactions. Our simulations showed that even a small local seed source greatly increases population growth rates, thereby balancing strong consumer pressure. The prevalence of strong negative interactions in the primary successional site is a reminder that successional communities will not exhibit the distribution of interaction strengths characteristic of stable communities, and suggests the potential utility of modeling succession as the consequence of interaction strengths.
Highlights
The extreme intensity of the disturbance that results in primary succession is generally considered to be responsible for the differences in community assembly between primary and secondary succession
In this study we asked three questions: 1) Does the limiting effect of multiple species interactions on plant reproduction vary with successional context? 2) Do consumers and mutualists differ in their influence on colonization during primary succession? and 3) How do successional differences in interactions combine with local control of propagule influx to affect colonization during primary succession? To address these questions, we investigated the effect of consumers and pollinator mutualists on black huckleberry (Vaccinium membranaceum) in primary successional and adjacent secondary successional areas created by the 1980 eruption of Mount St
In 2004, individuals in the primary successional population (PS) had a 23% increase in fruit set with pollen supplementation, whereas there was no increase in the secondary successional population (SS) (PS natural fruit set per plant: 0.7460.02 s.e.; PS supplemented: 0.9160.01 s.e.; SS natural: 0.760.15 s.e.; SS supplemented: 0.6760.15 s.e.)
Summary
The extreme intensity of the disturbance that results in primary succession is generally considered to be responsible for the differences in community assembly between primary and secondary succession. The effect of consumers on successional plant communities is regarded as more important in secondary succession [10,11] and in marine systems [12,13,14,15]. Because of their relative scarcity in primary succcesion, mutualists are thought to be more important in secondary succession, and the ability to grow and reproduce without their aid is considered an important attribute of primary successional plant colonists [8]. The temporary absence of mutualists, such as pollinators
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