Resource heterogeneity and persistence of exotic annuals in long-ungrazed Mediterranean-climate woodlands

Prober, Suzanne M.; Wiehl, Georg

doi:10.1007/s10530-011-0017-8

Cited by 24 publications

(35 citation statements)

References 54 publications

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“…Remnant woodlands have been affected to varying degrees by several aspects of land‐use intensification. In particular, many remnants have experienced eutrophication resulting from phosphate fertilizer drift, which is often accompanied by exotic annual grass and forb invasions (Dwyer et al, ; Prober & Wiehl, ). Still, though remnants are often invaded, many retain high native diversity and are composed of species‐rich novel communities of native and exotic annuals that co‐occur over local spatial scales (<0.09 m 2 ; Lai, Mayfield, Gay‐des‐combes, Spiegelberger, & Dwyer, ).…”

Section: Methodsmentioning

confidence: 99%

Distinct responses of niche and fitness differences to water availability underlie variable coexistence outcomes in semi‐arid annual plant communities

et al. 2018

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Climate change is predicted to have profound consequences for multispecies coexistence, and thus, patterns of biological diversity. These consequences will be mediated by direct and indirect impacts of environmental change on species’ vital rates and interactions. While the impacts of environmental change on individual species has received much attention to date, the consequences for coexistence mediated by changes in the strength and direction of multispecies interactions are not as well understood. To investigate how coexistence dynamics may be sensitive to environmental change, we conducted a field experiment in a diverse semi‐arid annual plant system. We imposed a water manipulation treatment in two sites that vary in aridity and associated rainfall. Focusing on four common annual plant species in these sites, we quantified the fecundity (seed production) of individuals in response to a gradient of intra‐ and interspecific competitor densities and aridity. We then used these fecundities to parameterize an annual plant population model and examine the influence of aridity and species identity on resultant coexistence dynamics (as a function of stabilizing niche differences and fitness inequalities). While the responses of some vital rates and competitive impacts to watering varied somewhat predictably across sites, coexistence metrics encapsulating changes in these vital rates and interaction strengths did not. Fitness inequalities among our focal species were driven largely by differences in sensitivity to competition, which were almost always much greater than the magnitude of stabilizing niche differences. These findings were surprising given observational evidence suggesting that these species do coexist at local scales in these natural communities. Synthesis. Our study is one of the first to explicitly consider the influence of environmental variation on the individual components of coexistence outcomes. We show that environmental change has the ability to influence coexistence not only through direct pathways (i.e., vital rates), but also indirect pathways (i.e., species interactions). Despite the consistency of many of the responses of these individual components to environmental variation, their combined influence on predictions of both current and future coexistence remains unclear.

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Section: Methodsmentioning

confidence: 99%

Distinct responses of niche and fitness differences to water availability underlie variable coexistence outcomes in semi‐arid annual plant communities

et al. 2018

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“…Canopies of York gum–jam woodlands are relatively open and are dominated by E. loxophleba and A. acuminata . Understories are composed of dense annual forb communities with a sparse shrub and perennial grass component (Dwyer et al., ; Prober & Wiehl, ). Although these understorey communities are often invaded, many are composed of species‐rich communities of native and exotic annuals that co‐occur over local spatial scales (<0.09 m 2 ; Lai, Mayfield, Gay‐des‐combes, Spiegelberger, & Dwyer, ).…”

Section: Methodsmentioning

confidence: 99%

Cyclic population dynamics and density‐dependent intransitivity as pathways to coexistence between co‐occurring annual plants

et al. 2018

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Recent studies have brought renewed attention to the importance of complex species interactions—notably intransitive interactions—to patterns of plant community diversity. One underappreciated avenue through which intransitivity can occur is through cyclic population dynamics. Although such cyclic intransitive relationships have been extensively studied in predator–prey systems, evidence of their importance in competitive communities, notably plant communities, is more limited. Most studies of coexistence in plant communities assume fixed‐point coexistence even while utilising models that allow for cyclic population dynamics. In this paper, we explore the potential for density‐dependent, cyclic population dynamics and intransitivity in a model for annual plants. We then examine how these density‐dependent cycles impact mutual invasibility and ultimately stable coexistence between plant species pairs. We do this using data collected from four co‐occurring annual plant species living in natural wildflower communities in SW Western Australia. To maximise the number of biologically plausible pathways by which coexistence mediated by density‐dependent cyclic intransitivity can occur, we use an annual plant model that allows for competitive direct interactions, facilitative direct interactions and higher‐order interactions between species. Results from our empirically parameterised model suggest that monocultures of all four focal species can have cyclic solutions with periodicity <1 under sunny (“open”) or shaded field conditions. Cyclic patterns drive variation in annual abundance patterns, with stable solutions for persistent monocultures and invasibility potential (the capacity of one population to invade another) common. Mutual invasibility in the face of cyclic population dynamics was found for just one of six species pairs, only under open environmental conditions. Our results illustrate the potential for cyclic intransitivity to both drive and prevent stable coexistence in environmentally heterogeneous biological communities. Synthesis. We provide analytical and empirical evidence that coexistence in competitive communities (annual plants) can be achieved under non‐equilibrium circumstances, through density‐dependent cyclic intransitivity. Our results suggest that cyclic population dynamics may be common and important for coexistence dynamics in some types of communities. In such communities, the exploration of stable coexistence should, therefore, include consideration of cyclic as well as fixed‐point equilibria for maximal accuracy.

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“…Relationships between soil nutrients and patch types are reported in Prober & Wiehl (2011) and summarized in Table S1 in Supporting Information. This study presents analyses of floristic composition and diversity of different native plant life‐forms in relation to soil nutrients, overstorey, mean winter rainfall and mean annual temperature.…”

Section: Methodsmentioning

confidence: 99%

“…, 2002a; Standish et al. , 2006; Prober & Wiehl, 2011) and that trees enhance soil carbon and nitrogen (Scholes & Archer, 1997; Prober et al. , 2002b; Prober & Wiehl, 2011).…”

Section: Methodsmentioning

confidence: 99%

Relationships among soil fertility, native plant diversity and exotic plant abundance inform restoration of forb‐rich eucalypt woodlands

Prober

Wiehl

2011

Diversity and Distributions

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Aim Water and nutrient availability are major limits to productivity in semi‐arid ecosystems; hence, ecological restoration often focuses on conserving or concentrating soil resources. By contrast, nutrient enrichment can promote invasion by exotic annuals, leading to restoration approaches that target reduction of soil nutrients. We aimed to explore potential biodiversity trade‐offs between these approaches by investigating relationships among soil nutrients, exotic annuals and native plant diversity and composition. In particular, we investigated the hypothesis that native plant diversity in semi‐arid to temperate woodlands reflects the productivity–diversity hypothesis, leading to hump‐backed relationships with soil nutrients such that (1) native plant diversity declines with increasing nutrient enrichment and (2) native diversity is limited at the lowest levels of soil fertility. Location Fragmented, long‐ungrazed Eucalyptus loxophleba subsp. loxophleba (York gum)–Acacia acuminata (jam) woodlands in the wheatbelt of South‐Western Australia. Methods We conducted stratified surveys of floristic composition and topsoil nutrient concentrations in 112 woodland patches. We used generalized linear models, structural equation models and ordinations to characterize relationships among soil nutrients, rainfall, exotic annuals and patch‐scale (100 m2) native plant composition and diversity. Results Patch‐scale native plant diversity declined strongly with increasing exotic abundance. This was partly related to elevated soil nutrient concentrations, particularly total nitrogen and available phosphorus. By contrast, there was little evidence for positive correlations between soil nutrients and native diversity, even at very low soil nutrient concentrations. Main conclusions Minimizing weed invasions is crucial for maximizing native plant diversity in E. loxophleba woodlands and could include nutrient‐depleting treatments without substantially compromising the functional capacity of soils to maintain native plant richness and composition. More broadly we emphasize that understanding relationships among ecosystem productivity, plant diversity and exotic invasions in the context of associated theoretical frameworks is fundamental for informing ecological restoration.

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Resource heterogeneity and persistence of exotic annuals in long-ungrazed Mediterranean-climate woodlands

Abstract: Processes that promote weed invasion are often well-demonstrated,

Cited by 24 publications

References 54 publications

Distinct responses of niche and fitness differences to water availability underlie variable coexistence outcomes in semi‐arid annual plant communities

Distinct responses of niche and fitness differences to water availability underlie variable coexistence outcomes in semi‐arid annual plant communities

Cyclic population dynamics and density‐dependent intransitivity as pathways to coexistence between co‐occurring annual plants

Relationships among soil fertility, native plant diversity and exotic plant abundance inform restoration of forb‐rich eucalypt woodlands

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