Dispersal mode mediates the effect of patch size and patch connectivity on metacommunity diversity

Theory describing the positive effects of patch size and connectivity on diversity in fragmented systems has stimulated a large body of empirical work, yet predicting when and how local species interactions mediate these responses remains challenging. We used insects that specialize on milkweed plants as a model metacommunity to investigate how local predation alters the effects of biogeographic constraints on species distributions. Species-specific dispersal ability and susceptibility to predation were used to predict when patch size and connectivity should shape species distributions, and when these should be modified by local predator densities. We surveyed specialist herbivores and their predators in milkweed patches in two matrix types, a forest and an old field. Predator-resistant species showed the predicted direct positive effects of patch size and connectivity on occupancy rates. For predator-susceptible species, predators consistently altered the impact of biogeographic constraints, rather than acting independently. Finally, differences between matrix types in species' responses and overall occupancy rates indicate a potential role of the inter-patch environment in mediating the joint effects of predators and spatial drivers. Together, these results highlight the importance of local top-down pressure in mediating classic biogeographic relationships, and demonstrate how species-specific responses to local and regional constraints can be used to predict these effects.

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“…, Jones et al. ). Thus, we used plant‐level occupancy to test whether insect densities, at the level of individual patches, differed.…”

Section: Methodsmentioning

confidence: 99%

Predators modify biogeographic constraints on species distributions in an insect metacommunity

Grainger

Germain

Jones

et al. 2017

Ecology

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“…Such interspecific dispersal differences result from different dispersal modes (active, passive and differences in vectors), dispersal abilities, or methods of habitat selection. These differences are an important feature of natural metacommunities (De Bie et al , Jones et al ) that can have major effects on local and regional coexistence and diversity (Amarasekare , Resetarits and Silberbush ). However, the most common method of manipulating dispersal (used by 42% of the studies reviewed here) eliminates these differences; researcher‐mediated bulk dispersal involves the transfer of part of a community among patches, for example a volume of water containing a portion of the community in aquatic studies (Fig.…”

Section: Incorporating Metacommunity Heterogeneitymentioning

confidence: 99%

Dispersal and diversity in experimental metacommunities: linking theory and practice

Grainger

Gilbert

2016

Oikos

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101

131

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There has been a recent rise in the number of experiments investigating the effect of dispersal on diversity, with many of the predictions for these tests derived from metacommunity theory. Despite the promise of linking observed relationships between dispersal and diversity to underlying metacommunity processes, empirical studies have faced challenges in providing robust tests of theory. We review experimental studies that have tested how dispersal affects metacommunity diversity to determine why shortcomings emerge, and to provide a framework for empirical tests of theory that capture the processes structuring diversity in natural metacommunities. We first summarize recent experimental work to outline trends in results and to highlight common methods that cause a misalignment between empirical studies and the processes described by theory. We then identify the undesired implications of three widely used experimental methods that homogenize metacommunity structure or species traits, and present alternative methods that have been used to successfully integrate experiments and theory in a biologically relevant way. Finally, we present methodological and theoretical insights from three related ecological fields (coexistence, food web and priority effects theory) that, if integrated into metacommunity experiments, could help isolate the independent and joint effects of local interactions and dispersal on diversity, and reveal the mechanisms underlying observed dispersal–diversity patterns. Together, these methods can provide stronger tests of existing theory and stimulate new theoretical explorations.

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“…, Jones et al. ). Despite its importance, dispersal ability is often an unknown parameter that is difficult to measure directly for many species.…”

Section: Introductionmentioning

confidence: 99%

Multiscale analysis of canopy arthropod diversity in a volcanically fragmented landscape

et al. 2019

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Habitat fragmentation resulting in habitat loss and increased isolation is a dominant driver of global species declines. Habitat isolation and connectivity vary across scales, and understanding how connectivity affects biodiversity can be challenging because the relevant scale depends on the taxa involved. A multiscale analysis can provide insight in biodiversity patterns across spatial scale when information on dispersal ability is not available, in particular for community‐level studies focusing on multiple taxa. In this study, we examine the relationship between arthropod diversity, patch area, and connectivity using a multiscale approach. We make use of a natural experiment on Hawai‘i Island, where historic volcanic activity has transformed contiguous native forests to lava matrix and discrete forest patches. This landscape of patches has persisted for 150 yr, and we selected 10,000 ha consisting of 863 patches to analyze landscape connectivity using a graph theory approach. We collected arthropod samples from Metrosideros polymorpha tree canopies in 34 forest patches during multiple years. We analyzed the relationship of arthropod diversity with area, as well as with connectivity across increasing scales, or dispersal threshold distances. In contrast to well‐established ecological theory as well as prior work on birds and fungi in this system, we did not find support for a canonical species–area relationship. Next, we calculated connectivity across spatial scales and found lower Shannon diversity with higher connectivity at small scales, but no effect at increased dispersal threshold distances. We examined the landscape structure and found all habitat patches connected into three subnetworks at a 350 m threshold distance. All patches were connected at 700 m threshold distance, indicating structural dispersal limitation only at small scales. Our findings suggest that canopy arthropods are not dispersal limited at scales shown to impact both soil fungi and birds in this system. Instead, Hawaiian canopy arthropods may perceive the landscape as a connected area where discrete forest patches and the early‐successional matrix contribute resources that vary spatially with regard to habitat quality. We argue for the utility of multiscale approaches, and the importance of examining maintenance of biodiversity in fragmented landscapes that persist for hundreds of years.

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Dispersal mode mediates the effect of patch size and patch connectivity on metacommunity diversity

Cited by 48 publications

References 57 publications

Predators modify biogeographic constraints on species distributions in an insect metacommunity

Predators modify biogeographic constraints on species distributions in an insect metacommunity

Dispersal and diversity in experimental metacommunities: linking theory and practice

Multiscale analysis of canopy arthropod diversity in a volcanically fragmented landscape

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