Species interactions affect dispersal: a meta-analysis

Abstract

Context-dependent dispersal allows organisms to seek and settle in habitats improving their fitness. Despite the importance of species interactions in determining fitness, a quantitative synthesis of how they affect dispersal is lacking. We present a meta-analysis asking (i) whether the interaction experienced and/or perceived by a focal species (detrimental interaction with predators, competitors, parasites or beneficial interaction with resources, hosts, mutualists) affects its dispersal; and (ii) how the species' ecological and biological background affects the direction and strength of this interaction-dependent dispersal. After a systematic search focusing on actively dispersing species, we extracted 397 effect sizes from 118 empirical studies encompassing 221 species pairs; arthropods were best represented, followed by vertebrates, protists and others. Detrimental species interactions increased the focal species' dispersal (adjusted effect: 0.33 [0.06, 0.60]), while beneficial interactions decreased it (-0.55 [-0.92, -0.17]). The effect depended on the dispersal phase, with detrimental interactors having opposite impacts on emigration and transience. Interaction-dependent dispersal was negatively related to species' interaction strength, and depended on the global community composition, with cues of presence having stronger effects than the presence of the interactor and the ecological complexity of the community. Our work demonstrates the importance of interspecific interactions on dispersal plasticity, with consequences for metacommunity dynamics.This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Keywords: biotic interactions; competition; context-dependent dispersal; host–parasite interactions; metacommunity dynamics; predator–prey interactions.

Figure 1.

The relationships between species interactions and dispersal. The dispersal of a focal species depends upon its biotic context, especially if the presence/abundance of an interacting species affects its fitness (grey arrows). In this meta-analysis, we extracted data from the literature to determine how the presence/abundance of the interacting species affects the dispersal of a focal species (black arrow). The relationship between interacting species’ presence/abundance and dispersal depends on the nature and strength of the biological interactors. Detrimental interactors such as predators, parasites or competitors (in red) negatively affect the fitness of the focal species (red − sign on the grey arrow). Because there is a negative relationship between fitness and dispersal (black − sign on the grey arrow), they should thus positively affect its dispersal (red + sign on the black arrow). On the other hand, beneficial interactors such as resources, hosts and mutualists (in blue) should positively affect the fitness (blue + sign on the grey arrow), and through the negative link between fitness and dispersal (black − sign), negatively affect dispersal (blue - sign on the black arrow). The effect of these interactions should depend on numerous biological regulators, related to the spatio-temporal co-dynamics and the ecological complexity, which affect the strength of interaction between species and thus the strength of interaction-dependent dispersal (green arrows). We translated these biological regulators into a number of statistical moderators (gold arrows) to explain the dependency of dispersal on the presence of an interacting species. By testing for these moderator effects on the relationship between the presence/abundance of the interacting species and dispersal of the focal species (gold and green arrows), we attempted to make inferences about the way fitness is affected by the interacting species and the way it affects the dispersal of the focal species (green arrows).

Figure 2.

The effect of interacting species on dispersal of the focal species depends on the type of interactor. Effect of (a) the type of interactor (red: detrimental interactors, blue: beneficial interactors) and (b) the nature of interactor (predator, competitor, parasite, resource, host and mutualist) on the effect of interacting species on dispersal (positive Hedges’ d values: increased dispersal in the presence of interactors, negative: decreased dispersal). Violin plots of raw effect sizes, with points and error bars corresponding to the marginal effect means and 95% CI from the two meta-analytic models for the subsets (i.e. beneficial and detrimental interactions; table 2, electronic supplementary material, table S5) and labels corresponding to the number of studies across moderators n and the number of effect sizes across categorical moderators k .

Figure 3.

The effect of interactors on focal species dispersal varies depending on the dispersal phase considered. Effect of the dispersal phase and the type of interactor (red: detrimental interactors, i.e. predators, competitors, parasites, blue: beneficial interactors, i.e. resources, hosts, mutualists) on the effect of interacting species on dispersal (positive Hedges’ d values: increased dispersal in the presence of interactors, negative: decreased dispersal). Violin plots of raw effect sizes, with point and error bars corresponding to the marginal effect means and 95% CI from the two meta-analytic models for the subsets (i.e. beneficial and detrimental interactions, table 2, electronic supplementary material, table S5), and labels corresponding to the number of effect sizes across categorical moderators k and the number of studies across moderators n.

Figure 4.

For detrimental interactions, the effect of interacting species on focal species dispersal varies depending on the biotic context. Effect of (a) the type of manipulation of the interactor (i.e. presence, cues of presence or abundance) and (b) the level of community complexity (pairs of species, simple community, complex community) on the effect of detrimental interactors on dispersal (positive Hedges’ d values: increased dispersal in the presence of interactors, negative: decreased dispersal). Violin plots of raw effect sizes, with point and error bars corresponding to the marginal effect means and 95% CI from the meta-analytic model for the detrimental interactors data subset (table 2, electronic supplementary material, table S5), and labels corresponding to the number of effect sizes across categorical moderators k and the number of studies across moderators n.

Figure 5.

The effect of interactors on focal species dispersal varies depending on both species’ level of generalism. Effect of the generalism of (a) the focal species or (b) the interactor and type of interactor (red: detrimental, blue: beneficial) on the effect of interacting species on dispersal (positive Hedges’ d values: increased dispersal in the presence of interactors, negative: decreased dispersal). The level of generalism is rated from 1 to 4 on whether species interact only with one species (1), with species from the same genus or family (2), with species from the same order (3), or with species from different orders (4). Points represent the effect sizes, and lines and confidence intervals are displayed from marginal means and 95 % CI from the two meta-analytic models calculated at the four levels of generalism.

Figure 6.

The effect of interactors on focal species dispersal varies on the strength of interaction between species. Effect of the interaction strength between pair of species and type of interactor (red: detrimental, blue: beneficial) on the effect of interacting species on dispersal (positive Hedges’ d values: increased dispersal in the presence of interactors, negative: decreased dispersal), for the 357 effect sizes for which we could retrieve interaction strength. Coloured points represent interaction strength as a function of Hedges’d, for either the subset of data for which interaction strength was measured concomitantly to dispersal (‘strict database’, triangles, 166 es), for which the interaction strength was found in the secondary literature (upside-down triangles, 191 es), or for which the interaction strength was not found at all and thus is only categorized as positive or negative (crosses, 40 es). Lines and ribbons represent the effect of interaction strength on dispersal from the meta-analytic model, either on the strict database (dashed line, electronic supplementary material, table S7), or on all measures of interaction strength (full line, electronic supplementary material, table S7).