Outcome Of Biotic Interactions Research Articles

Ecological convergence in phytochemistry and flower-insect visitor interactions along an Andean elevation gradient.

The diversity of specialized molecules produced by plants radiating along ecological gradients is thought to arise from plants' adaptations to local conditions. Therefore, closely related species growing in similar habitats should phylogenetically converge, or diverge, in response to similar climates, or similar interacting animal communities. We here asked whether closely related species in the genus Haplopappus (Asteraceae) growing within the same elevation bands in the Andes, converged to produce similar floral odors. To do so, we combine untargeted analysis of floral volatile organic compounds with insect olfactory bioassay in congeneric Haplopappus (Asteraceae) species growing within the same elevation bands along the Andean elevational gradient. We then asked whether the outcome of biotic interactions (i.e., pollination vs. seed predation) would also converge across species within the same elevation. We found that flower odors grouped according to their elevational band and that the main floral visitor preferred floral heads from low-elevation band species. Furthermore, the cost-benefit ratio of predated versus fertilized seeds was consistent within elevation bands, but increased with elevation, from 6:1 at low to 8:1 at high elevations. In the light of our findings, we propose that climate and insect community changes along elevation molded a common floral odor blend, best adapted for the local conditions. Moreover, we suggest that at low elevation where floral resources are abundant, the per capita cost of attracting seed predators is diluted, while at high elevation, sparse plants incur a higher herbivory cost per capita. Together, our results suggest that phytochemical convergence may be an important factor driving plant-insect interactions and their ecological outcomes along ecological gradients.

Modeling the continua in the outcomes of biotic interactions.

The outcome of many ecological interactions lies somewhere along a continuum between pure positive and pure negative effects. Although the popularity of this idea has notoriously risen in the last decades, with the occurrence of continua in interaction outcomes invoked for a wide variety of interactions, the absence of a precise theoretical treatment has led to considerable inaccuracy and ambiguity in its treatment. We develop here a consumer-resource model to explore the occurrence of continua. This model is based on the assumption that the distribution of individual interaction events includes both negative and positive immediate outcomes, with variable frequencies, for at least one of the interacting species. Our study shows that continua in interaction outcomes happen just by varying the sign and impact of individual events. The exact shape of the continua depends on the proportion of positive versus negative events and the relative magnitude of per-capita interaction strengths. Our model shows that continua in interaction outcomes are a key property of most pairwise interactions and are originated from the variable roles played by the interacting partners. It constitutes a step forward in the paradigm change from discrete categorization of ecological interactions to a new perspective over a continuous space.

Testing the role of functional trait expression in plant–plant facilitation

AbstractPositive biotic interactions between plant species may strongly affect species and community‐level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that plant–plant facilitation could occur through the impact of benefactor species on the functional trait expression of beneficiary species. Indeed, plant species that affect local conditions can modify functional trait expression of interacting species, thereby improving their performance and resulting in a facilitative interaction. However, the response of intraspecific trait variation to biotically driven microhabitat modification, and its role in determining the outcome of plant–plant interactions, has rarely been explored.Here, we test whether growing with benefactor species affects the expression of functional traits of eight species, encompassing different plant growth forms, in two contrasting study systems. This is achieved using a paired sampling approach to compare values of seven functional traits of conspecific individuals growing within and adjacent to cushion plants (i.e. benefactor species which are known to strongly alter microhabitat conditions and to have positive effects on some of the focal species). In addition, we test whether the effect of biotic interactions on functional trait expression changes along elevational gradients, as the outcome of biotic interactions is expected to vary with elevation.Contrary to predictions, in both systems, intraspecific trait variation was not well explained by the biotic interaction with the cushion plant species or the variation in abiotic conditions associated with elevational gradients. Where biotic interactions did affect functional trait expression and bivariate trait relationships, traits responded variably between species, suggesting that context specificity may be a constraint to predicting how intraspecific trait variation responds to plant–plant interactions, adding to the growing body of literature that challenges the generality and predictability of the drivers of intraspecific trait variation.This research, therefore, suggests that benefactor species’ facilitative process is likely not through an impact on intraspecific trait expression, and that instead other processes may be more important for translating beneficial microhabitat modification or increased resource availability by benefactor species into positive impacts on beneficiary species.A freePlain Language Summarycan be found within the Supporting Information of this article.

Phylogenetic signals and predictability in plant-soil feedbacks.

Summary There is strong evidence for a phylogenetic signal in the degree to which species share co‐evolved biotic partners and in the outcomes of biotic interactions. This implies there should be a phylogenetic signal in the outcome of feedbacks between plants and the soil microbiota they cultivate. However, attempts to identify a phylogenetic signal in plant–soil feedbacks have produced mixed results.Here we clarify how phylogenetic signals could arise in plant–soil feedbacks and use a recent compilation of data from feedback experiments to identify: whether there is a phylogenetic signal in the outcome of plant–soil feedbacks; and whether any signal arises through directional or divergent changes in feedback outcomes with evolutionary time.We find strong evidence for a divergent phylogenetic signal in feedback outcomes. Distantly related plant species show more divergent responses to each other’s soil microbiota compared with closely related plant species. The pattern of divergence implies occasional co‐evolutionary shifts in how plants interact with soil microbiota, with strongly contrasting feedback responses among some plant lineages.Our results highlight that it is difficult to predict feedback outcomes from phylogeny alone, other than to say that more closely related species tend to have more similar responses.

Testing for consistency in ecosystem engineering: Do cushion plants always turn up the heat?

Ecosystem engineers influence community structure and functioning by altering habitat and resource availability. However, few studies have assessed how consistent ecosystem engineers' impacts are on abiotic habitat conditions and/or community characteristics, either across species or between habitats. Here we test for the consistency of ecosystem engineering across, and within, cushion-forming plant species, a group of ecosystem engineers that are dominant in polar and alpine environments, by reviewing studies that document their effects on temperature. We find inconsistent effects, with cushion plants having contrasting impacts on temperatures in different studies. Even after limiting analyses to a single cushion plant morphology type or to just a single species, impacts on temperature were still inconsistent between studies. Therefore, while cushion plants have relatively consistent impacts on plant communities (e.g. increasing local species richness), their impact on temperature may not be the overarching abiotic mechanism driving this ecological effect. These results, therefore, highlight the need to explicitly test if ecosystem engineers’ biotic and abiotic impacts are consistent through space and time, and emphasize the importance of understanding context-dependence in the outcome of biotic interactions.

Mutualism or parasitism: Partner abundance affects host fitness in a fish reproductive interaction

Abstract Mutualisms are ubiquitous in nature but are understudied in freshwater ecosystems. Mutualisms can be unstable, shifting to commensal or even negative outcomes with context. Quantifying context dependency in mutualisms is critical for understanding how biotic interactions will shift along disturbance gradients in freshwater systems. A common reproductive interaction among stream fishes, nest association occurs when individuals of one species spawn in nests constructed by a host fish. Hosts benefit from a dilution effect: high proportions of associate eggs decrease the odds of host brood predation. Thus, partner abundance can be an important source of biotic context influencing the outcome of an association. We conducted a large in situ experiment manipulating abundance of partner yellowfin shiner (Leuciscidae: Notropis lutipinnis) (absent, low, high) at constant abundance of host bluehead chub (Leuciscidae: Nocomis leptocephalus), and quantified chub reproductive success using genetic tools. Evidence suggests that the nest association switched from mutualistic to parasitic outcomes as shiner abundance decreased. Chub reproductive success was highest at high shiner abundances. However, chub reproductive success was actually higher in the complete absence of shiners than at low shiner densities. This study shows that outcomes of biotic interactions in freshwater systems are context‐dependent, and that partner abundance can be a key source of context‐dependency in nest associations. We encourage future studies on freshwater mutualisms, which are thus far largely overlooked, relative to competition and predation.

The fitness benefits of germinating later than neighbors.

Phenology, the seasonal timing of development, can alter biotic interactions. Emergence from dormant or quiescent stages often occurs earlier when neighbors are present, which may reduce the neighbors' competitive effects. Delayed emergence in response to neighbors also has been observed, but the potential benefits of such delays are unclear. Further, emergence time may respond to neighbors experienced by parents, which may predict future competition in offspring. In the annual plant Arabidopsis thaliana (Brassicaceae), we quantified seed germination responses to neighbors in parental and offspring (seed) environments. To examine how observed changes in germination affect interactions with neighbors, we performed an outdoor experiment using neighbors of different sizes to represent different germination times. Seeds were more likely to germinate if their parent had neighbors, but they were less likely to germinate if they themselves experienced a neighbor cue (canopy). As seeds lost dormancy over time, they gained the ability to germinate under a canopy, which suggests that they germinate later in the presence of neighbors. Neighbors of both sizes reduced growth, survival to reproduction, fecundity, and total fitness, but large neighbors increased seedling survival. Smaller neighbors provided no such benefit and had stronger negative effects. Delayed germination in response to neighbors can reduce negative interactions and promote positive ones if it occurs late enough to expose seedlings to larger neighbors. By altering relative phenologies and, in turn, the outcomes of biotic interactions, phenological responses to environmental change may influence species interactions and community dynamics.

The Interplay Between Landscape Structure and Biotic Interactions

Landscape structure and biotic interactions are closely linked. We identify five aspects of landscape structure that contribute to the co-occurrence of species and restrict or enable different types of biotic interactions: patch size and habitat amount, isolation of patches, barriers to dispersal and movement, persistence of landscape structure, and landscape complexity. In addition, these aspects of landscape structure influence the strength and outcome of biotic interactions. Whereas most research focuses on the effects of the abiotic environment on species and their biotic interactions, research on foundation species and ecosystem engineers demonstrates the important influence of biotic interactions on landscape structure itself, including effects on landscape complexity, extent of habitat, and the structure of landscape features. In this review, we describe ecological theories that lay the foundation for interplay between landscape structure and biotic interactions, and summarize these connections across an array of interacting species in freshwater, marine, and terrestrial systems. We end with suggestions for integrating the fields of landscape ecology and community ecology to better understand the connections between landscape structure and biotic interactions and better predict their dynamics in light of global change.

Community assembly, coexistence and the environmental filtering metaphor

Summary One of the most pervasive concepts in the study of community assembly is the metaphor of the environmental filter, which refers to abiotic factors that prevent the establishment or persistence of species in a particular location. The metaphor has its origins in the study of community change during succession and in plant community dynamics, although it has gained considerable attention recently as part of a surge of interest in functional trait and phylogenetic‐based approaches to the study of communities. While the filtering metaphor has clear utility in some circumstances, it has been challenging to reconcile the environmental filtering concept with recent developments in ecological theory related to species coexistence. These advances suggest that the evidence used in many studies to assess environmental filtering is insufficient to distinguish filtering from the outcome of biotic interactions. We re‐examine the environmental filtering metaphor from the perspective of coexistence theory. In an effort to move the discussion forward, we present a simple framework for considering the role of the environment in shaping community membership, review the literature to document the evidence typically used in environmental filtering studies and highlight research challenges to address in coming years. The current usage of the environmental filtering term in empirical studies likely overstates the role abiotic tolerances play in shaping community structure. We recommend that the term ‘environmental filtering’ only be used to refer to cases where the abiotic environment prevents establishment or persistence in the absence of biotic interactions, although only 15% of the studies in our review presented such evidence. Finally, we urge community ecologists to consider additional mechanisms aside from environmental filtering by which the abiotic environment can shape community pattern.

Outcomes of biotic interactions are dependent on multiple environmental variables

AbstractQuestionCan variation in the outcome of biotic interactions in relation to environmental severity be more accurately predicted when considering multiple stress and/or disturbance variables?LocationArctic‐alpine tundra in Kilpisjärvi, North Finland.MethodsTo test the impact of including multiple environmental variables in analyses of the outcomes of biotic interactions, we modelled reproductive effort and cover of 17 arctic‐alpine species as a function of Empetrum nigrum subsp. hermaphroditum cover, geomorphological disturbance and soil moisture with statistical interactions of the explanatory variables included. We implemented a best‐subset approach using generalized linear models (GLM) and selected the best model for each species based on Akaike's information criterion (AIC).ResultsFor the majority of species, models including multiple environmental variables were selected as best. Reproductive effort depended on one or both environmental variables for all species, and 14 species were additionally influenced by Empetrum, with the impact of Empetrum varying with abiotic conditions in all but one of those species. Moreover, the three‐way interaction of three explanatory variables was included in the best‐fit models for six species. The impact of Empetrum on species cover showed a similar pattern, with 11 species affected by Empetrum and its statistical interactions with one or both abiotic variables.ConclusionsBiotic interactions have an important role in arctic‐alpine vegetation, but to fully understand variation in their effects multiple environmental factors should be explicitly considered. In this study, the outcome of biotic interactions was frequently dependent on two abiotic variables (and occasionally additionally on their statistical interaction). Therefore, we demonstrate that studies based on only one environmental factor may cause misleading interpretations of the nature of biotic interactions in plant communities where there are multiple independent variables underlying the habitat severity gradient.

Biotic interactions drive species occurrence and richness in dynamic beach environments

Biotic interactions are predicted to have the strongest influence on species assemblages in extreme environments. We therefore test the hypothesis that in abiotically-severe beaches plant–plant interactions, specifically facilitation, are important relative to abiotic conditions. This hypothesis is tested by assessing the influence of dominant vascular plant species on the fine-scale occurrence and richness of vascular and cryptogam species using a unique dataset of boreal beaches along the Finnish Baltic Sea, characterized by strong post-glacial land uplift and large environmental gradients. We studied three different levels of vegetation patterns across a broad geographical scale; individual species, functional groups and the entire community. Results showed that dominant vascular species strongly drive species occurrence and richness in dynamic beach environments, with some species having an influence similar to that of key abiotic variables. In contrast to expectations, facilitative effects did not dominate in these harsh environments. Instead, the outcomes of biotic interactions were species-specific, and also differed between vascular and cryptogam species, with the former group most strongly influenced by a pioneer species and the latter by a late succession generalist. Our study highlights the importance of incorporating biotic interaction effects into models of multiple vegetation properties and cautions against overly simplistic generalizations to describe relatively idiosyncratic interaction effects.

Interactive Effects of Resources and a Processing Chain Interaction in Treehole Habitats

The degree to which the outcome of biotic interactions is sensitive to resource levels is a fundamental issue in ecology. Conversely, resource availability may be affected by processing chain interactions, where organisms specialize on a resource in different states of decay. An organism upstream in the decay sequence can affect availability of resources to downstream consumers. Experimental microcosms that mimic tree-hole habitats were used to test the hypothesis that leaf-shredders process resources and facilitate populations of downstream consumers under conditions of resource limitation in a detritus-based community. Resources were varied independently of presence of leaf-shredding scirtid beetles (Helodes pulchella and Prionocyphon discoideus) to examine interactions among resource level, scirtids, and the mosquito Aedes triseriatus. Scirtids facilitated growth of A. triseriatus only when resource quantity was low. Survival of mosquitoes was negatively affected by the lowest resource level only when scirtids were absent. At the highest resource levels, scirtids hindered growth of mosquitoes in comparison to high resources without scirtids. Leaf-shredders affect resource availability, and resource processing by scirtids has significant repercussions on populations of A. triseriatus that are dependent upon resource level. Although resources alone had large effects on mosquito growth, these bottom-up effects were conditionally mediated by shredders.