Functional tradeoffs determine species coexistence via the storage effect. Proc Natl Acad Sci USA

Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2009; 106(28):11641-5. DOI: 10.1073/pnas.0904512106
Source: PubMed


How biological diversity is generated and maintained is a fundamental question in ecology. Ecologists have delineated many mechanisms that can, in principle, favor species coexistence and hence maintain biodiversity. Most such coexistence mechanisms require or imply tradeoffs between different aspects of species performance. However, it remains unknown whether simple functional tradeoffs underlie coexistence mechanisms in diverse natural systems. We show that functional tradeoffs explain species differences in long-term population dynamics that are associated with recovery from low density (and hence coexistence) for a community of winter annual plants in the Sonoran Desert. We develop a new general framework for quantifying the magnitude of coexistence via the storage effect and use this framework to assess the strength of the storage effect in the winter annual community. We then combine a 25-year record of vital rates with morphological and physiological measurements to identify functional differences between species in the growth and reproductive phase of the life cycle that promote storage-effect coexistence. Separation of species along a tradeoff between growth capacity and low-resource tolerance corresponds to differences in demographic responses to environmental variation across years. Growing season precipitation is one critical environmental variable underlying the demographic decoupling of species. These results demonstrate how partially decoupled population dynamics that promote local biodiversity are associated with physiological differences in resource uptake and allocation between species. These results for a relatively simple system demonstrate how long-term community dynamics relate to functional biology, a linkage scientists have long sought for more complex systems.

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    • "ect ( Chesson , 2000 ) , when inter - annual variation in climate or resource availability favors alternatively one group of species over the others ( e . g . , Zavaleta et al . , 2003 ) . Not only inter - annual but also seasonal variability contributes to fluctuating resources that increase the number of coexisting species in different systems ( Angert et al . , 2009 ; Shimadzu et al . , 2013 ) . Oscillations at the population level"
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    ABSTRACT: The consequences of global change for the maintenance of species diversity will depend on the sum of each species responses to the environment and on the interactions among them. A wide ecological literature supports that these species-specific responses can arise from factors related to life strategies, evolutionary history and intraspecific variation, and also from environmental variation in space and time. In the light of recent advances from coexistence theory combined with mechanistic explanations of diversity maintenance, we discuss how global change drivers can influence species coexistence. We revise the importance of both competition and facilitation for understanding coexistence in different ecosystems, address the influence of phylogenetic relatedness, functional traits, phenotypic plasticity and intraspecific variability, and discuss lessons learnt from invasion ecology. While most previous studies have focused their efforts on disentangling the mechanisms that maintain the biological diversity in species-rich ecosystems such as tropical forests, grasslands and coral reefs, we argue that much can be learnt from pauci-specific communities where functional variability within each species, together with demographic and stochastic processes becomes key to understand species interactions and eventually community responses to global change.
    Frontiers in Plant Science 11/2015; 6. DOI:10.3389/fpls.2015.00866 · 3.95 Impact Factor
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    • "The environment experienced by individuals in these communities routinely fluctuates because resource accessibility is dynamic in space and time. Such environmental fluctuations can facilitate competitor coexistence if functional trade-offs cause species to vary in their competitive superiority (e.g., Yu and Wilson 2001; Angert et al. 2009; Holt and Chesson 2014). We previously showed how fluctuating patch accessibility leads to coexistence among ephemeral patch competitors, given a trade-off between fecundity and dispersal ability (Duthie et al. 2014). "
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    ABSTRACT: The ecological principle of competitive exclusion states that species competing for identical resources cannot coexist, but this principle is paradoxical because ecologically similar competitors are regularly observed. Coexistence is possible under some conditions if a fluctuating environment changes the competitive dominance of species. This change in competitive dominance implies the existence of trade-offs underlying species’ competitive abilities in different environments. Theory shows that fluctuating distance between resource patches can facilitate coexistence in ephemeral patch competitors, given a functional trade-off between species dispersal ability and fecundity. We find evidence supporting this trade-off in a guild of five ecologically similar nonpollinating fig wasps and subsequently predict local among-patch species densities. We also introduce a novel colonization index to estimate relative dispersal ability among ephemeral patch competitors. We suggest that a dispersal ability–fecundity trade-off and spatiotemporally fluctuating resource availability commonly co-occur to drive population dynamics and facilitate coexistence in ephemeral patch communities.
    The American Naturalist 05/2015; 186(1). DOI:10.1086/681621 · 3.83 Impact Factor
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    • "In this context, temporal increases in water availability are very likely to alter the functional structure of annual plant communities, by selecting for species with higher growth rates over species that can tolerate low resource levels (Angert et al. 2009). Moreover, given that the effect of grazing is strongly mediated by resource availability (D ıaz et al. 2007a; Carmona et al. 2012, 2013), increased water availability is also likely to affect the patterns of functional structure across grazing gradients, by enhancing the abundance of grazing-tolerant species along grazing gradients . "
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    ABSTRACT: QuestionsHow do inter-annual fluctuations in water availability affect the functional trait patterns along spatial gradients of resource availability and disturbance?LocationMediterranean grasslands in central Spain, near Madrid.Methods We surveyed plant communities from 66 sites under different grazing regimes (from heavy grazing to grazing abandonment) in productive and unproductive habitats (corresponding to upper and lower topographic zones) in 2 yr with contrasting rainfall conditions. Community weighted mean (CWM) and Rao quadratic entropy for three key plant ecological strategy traits (specific leaf area, height and seed mass) were calculated for each community. We used null models to estimate functional richness (FR) and functional divergence (FD), the two components of functional diversity with the highest power to detect changes in community assembly processes across environmental gradients.ResultsThe patterns of CWM remained rather constant across years, with the only exception being seed mass, which experienced considerable temporal changes that suggested that heavy-seeded species are favoured under stressful conditions. Patterns for FR were consistent across years. They revealed both trait convergence and divergence depending on the niche axis and context. Convergence was observed for vegetative traits in unproductive habitats and seed mass in productive ones, and divergence for seed mass in unproductive habitats and vegetative traits in productive ones. In contrast, the patterns of FD of the vegetative traits changed considerably between years, as shown by increased divergence during the wet year in unproductive habitats and decreased divergence in grazing-abandoned productive habitats.Conclusions Temporal changes in Mediterranean grassland composition depend on complex interactions between species traits, resource availability and disturbance. Increased rainfall appeared to have contrasting effects on assembly processes in stressful and productive habitats. In stressful habitats we found evidence that increased rainfall promoted niche complementarity, while in productive habitats, especially in the absence of disturbance, it increased trait convergence.
    Journal of Vegetation Science 11/2014; 26(3). DOI:10.1111/jvs.12260 · 3.71 Impact Factor
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