Sedgwick Reserve

30 Jun, 11 PM - 30 Aug, 10 PM

One of most enduring mysteries in ecology is how multiple plant species, all competing for the same handful of limiting resources, coexist. For many decades, ecologists believed that niche differences among species were critical to their long term coexistence. This idea has been recently challenged by neutral models, which assume that species are functionally identical. Species co-occur for long periods of time in neutral models because their eventual stochastic drift to extinction is a slow process. These ideas have generated controversy because they suggest that the niche differences among species, long thought to be critical for coexistence, may not be so important. Nonetheless, the polarizing nature of the ?niche? vs. ?neutral? debate has obscured the fact that both the degree of fitness equivalence (neutrality) and the strength of stabilizing processes (niches) drive coexistence. Theory shows that coexistence arises when niche differences are large enough to overcome differences in average fitness among species. Unfortunately, we have little understanding of whether coexistence in natural communities results from strong stabilizing processes (?Niche Theory?) overcoming large fitness differences among species versus weak stabilization combined with high fitness equivalence (?Neutral Theory?). The proposed work addresses this critical gap by quantifying the contribution of ?niches? and ?neutrality? to the coexistence of California serpentine annual plants. The research team, consisting of three young plant ecologists, has developed a novel approach to this problem which involves quantifying and manipulating the relationship between species per capita growth rates and their relative frequency in the community. Declines in population growth with increasing frequency are the hallmark of stabilizing processes (niches), while fitness equivalence (neutrality) is represented by the differences among species in their population growth rates when rare. In the first proposed experiment, the strength of stabilizing processes and the degree of fitness equivalence are quantified for 10 serpentine annual plants by measuring how their per capita growth rates vary with frequency in experimental communities. In the second experiment, stabilizing processes (niches) are removed by manipulating population growth rates so that species no longer suffer reductions in growth as they become more frequent. Extinction dynamics in these communities are compared to dynamics in control communities experiencing their natural degree of stabilization. This second experiment evaluates how long species co-occur when their dynamics are only subject to species differences in fitness and demographic stochasticity. Finally, the degree of fitness equivalence and stabilizing processes in natural serpentine annual plant communities will be assessed by quantifying the demography of co-occurring annuals across natural variation in their frequency over space and time.

Visit #11332 @Sedgwick Reserve

Approved

Under Project # 5611 | Research

California annual serpentine communities

faculty - University of Washington

Reservation Members(s)

Janneke Hillerislambers Jun 30 - Aug 30, 2006 (62 days)
Group of 3 Faculty Jun 30 - Aug 30, 2006 (62 days)
Group of 3 Undergraduate Student Jun 30 - Aug 30, 2006 (62 days)

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