A shift from exploitation to interference competition with increasing density affects population and community dynamics

Holdridge, Erica M.; Cuellar-Gempeler, Catalina; terHorst, Casey P.

doi:10.1002/ece3.2284

Cited by 35 publications

(28 citation statements)

References 59 publications

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“…These positive relationships might arise because of negligible negative effects of competitive interactions on individual productivity, or, in fungal-specific cases, potentially due to greater investment in defensive activities that increase biomass [i.e., defensive wall building to prevent overgrowth by competitors (31)]. Quantifying the relative influences of exploitative versus interference competition may help to resolve why such a broad range of diversity-function relationships is observed for fungal communities (22,24,25,33).…”

Section: Resultsmentioning

confidence: 99%

Competitive network determines the direction of the diversity–function relationship

Maynard

Crowther

Bradford

2017

Proc. Natl. Acad. Sci. U.S.A.

116

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The structure of the competitive network is an important driver of biodiversity and coexistence in natural communities. In addition to determining which species survive, the nature and intensity of competitive interactions within the network also affect the growth, productivity, and abundances of those individuals that persist. As such, the competitive network structure may likewise play an important role in determining community-level functioning by capturing the net costs of competition. Here, using an experimental system comprising 18 wood decay basidiomycete fungi, we test this possibility by quantifying the links among competitive network structure, species diversity, and community function. We show that species diversity alone has negligible impacts on community functioning, but that diversity interacts with two key properties of the competitive networkcompetitive intransitivity and average competitive ability-to ultimately shape biomass production, respiration, and carbon use efficiency. Most notably, highly intransitive communities comprising weak competitors exhibited a positive diversity-function relationship, whereas weakly intransitive communities comprising strong competitors exhibited a negative relationship. These findings demonstrate that competitive network structure can be an important determinant of community-level functioning, capturing a gradient from weakly to strongly competitive communities. Our research suggests that the competitive network may therefore act as a unifying link between diversity and function, providing key insight as to how and when losses in biodiversity will impact ecosystem function.competitive intransitivity | basidiomycete | interference | community assembly | ecosystem function T he relationship between biological diversity and ecosystem functioning is a central question in ecology and conservation, providing tangible links between natural systems and the provision of ecosystem services to humans. In recent decades, a wealth of studies have explored how ecosystem functioning responds to changes in various types of diversity (e.g., species, trait, or phylogenetic diversity), revealing the highly idiosyncratic nature of this relationship across systems (1). Functionally unique species with mutually exclusive resource requirements can exhibit greater productivity in diverse communities (2), whereas highly similar species with overlapping niches exhibit minimal increases in functioning as diversity increases (1, 3). Although the field of biodiversity-ecosystem function (BEF) research continues to gain momentum, the sheer complexity of ecological communities complicates the search for unifying patterns (1). As such, in most systems, we still lack the ability to predict a priori how changes in biodiversity will alter ecosystem function.The BEF relationship is often linked to the degree of functional redundancy, complementarity, or niche overlap among species (4-6). Yet this relationship can alternatively be formulated in terms of the nature, variability, and intensity of ...

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Section: Resultsmentioning

confidence: 99%

Competitive network determines the direction of the diversity–function relationship

Maynard

Crowther

Bradford

2017

Proc. Natl. Acad. Sci. U.S.A.

116

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“…These data suggest that cell size and peak density may evolve independently of one another or that different mechanisms of competitive ability (e.g., exploitation vs. interference; Holdridge et al. ) are advantageous in different resource environments.…”

Section: Discussionmentioning

confidence: 92%

“…In high nutrient environments, Colpidium populations were more dense (Appendix S4: Fig. S1) and likely experienced more intense intraspecific competition (Holdridge et al 2016). This could be the selective agent driving the increase in cell size in the historical high nutrient environment.…”

Section: Discussionmentioning

confidence: 99%

Predator trait evolution alters prey community composition

2017

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Abstract. Predators have potentially strong effects on prey abundance, growth, life histories, and behavior, but the net direction and strength of these effects depend on traits in the predator population. Trait evolution that occurs on ecological timescales is common and may affect species interactions. Using laboratory microcosms of a bacterivorous ciliate (Colpidium sp.) and a diverse community of bacteria, we tested the hypothesis that predator trait evolution in response to temperature variability and nutrient concentration alters the composition of the prey community using a two-phase experiment. The first phase consisted of a selection experiment, in which microcosm communities were randomly assigned to one of eight fully factorial treatments of high or low nutrients, variable or stable temperatures, and with or without Colpidium. The second phase was a reciprocal transplant experiment, in which a subsample of each microcosm community from the selection experiment was transferred to one of four common garden environments, consisting of all combinations of high or low nutrients and variable or stable temperature. Nutrient enrichment directly decreased bacterial species richness and altered the community composition, but also indirectly increased bacterial species richness through decreases in ciliate peak density and, subsequently, ciliate abundance. Moreover, the evolutionary effects of nutrient enrichment on predator traits were more pronounced in some contemporary common garden environments, and undetectable in others. Our findings suggest that historical and contemporary environments are equally important to consider in understanding how trait evolution affects community structure.

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“…Furthermore, the benefits of increasing resource abundance may diminish at high consumer densities when interference is the predominant mode of competition. For example, protozoans switch from exploitative to interference competition as conspecific density increases, and this competition is not alleviated by an increase in basal resources (Holdridge, Cuellar‐Gempeler, & terHorst, ). Similarly, a 45% increase in barnacle density did not alleviate snail competition in our experiment, further supporting our hypothesis that interference played a key role in snail competition.…”

Section: Discussionmentioning

confidence: 99%

Cascading effects of a top predator on intraspecific competition at intermediate and basal trophic levels

2018

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Predators can impact competition among prey by altering prey density via consumption or by causing prey to modify their traits or foraging behavior. Yet, differences between these two mechanisms may lead to different cascading impacts on lower trophic levels. Using a crab‐snail‐barnacle rocky intertidal food chain, we tested the effects of predation risk from crabs (top predators) on intraspecific competition among snails (intermediate consumers) and emergent indirect effects on the density of and competition among barnacles (basal resources). The per capita foraging and growth rates of snails declined with high conspecific density. Predation risk from crabs, which caused even larger reductions in snail foraging and growth, weakened competition among snails, whereas a 45% increase in barnacle density had no detectable effect on snail competition. Intraspecific competition between barnacles, however, depended on the interactive effects of barnacle density, snail density, and crab predation risk. Barnacles developed hummocking morphologies as they grew and competed for space. Hummock formation (a proxy for competition) increased as a result of either greater initial barnacle density or reduced snail foraging pressure, but these effects depended on predation risk. The effects of crab predation risk on snail foraging behavior weakened an otherwise strong relationship between barnacle density and hummock development: hummocking increased with barnacle density in the absence of crabs but remained relatively high when crabs were present. In communities with similar final barnacle densities, hummocking was more common in those with crabs than those without crabs. The extent to which predators can drive trophic cascades by suppressing the foraging rates of their prey is highly context‐dependent: the positive trait‐mediated indirect effect of predators on basal resource abundance is stronger when many prey respond simultaneously to the threat of predation. However, our results demonstrate that top predators can also enhance competition among basal resources even when their indirect effect on resource abundance is relatively weak. Hence, the cascading effects of predators on competition within lower trophic levels may play an important but under‐appreciated role in the dynamics of basal resource populations and the communities they support. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13131/suppinfo is available for this article.

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A shift from exploitation to interference competition with increasing density affects population and community dynamics

Cited by 35 publications

References 59 publications

Competitive network determines the direction of the diversity–function relationship

Competitive network determines the direction of the diversity–function relationship

Predator trait evolution alters prey community composition

Cascading effects of a top predator on intraspecific competition at intermediate and basal trophic levels

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