Impacts of habitat connectivity on grassland arthropod metacommunity structure: A field-based experimental test of theory

Abstract

Metacommunity theory has advanced scientific understanding of how species interactions and spatial processes influence patterns of biodiversity and community structure across landscapes. While the central tenets of metacommunity theory have been promoted as pivotal considerations for conservation management, few field experiments have tested the validity of metacommunity predictions. Here, we tested one key prediction of metacommunity theory-that decreasing habitat connectivity should erode metacommunity structure by hindering species movement between patches. For 2 years, we manipulated an experimental old-field grassland ecosystem via mowing to represent four levels of habitat connectivity: (1) open control, (2) full connectivity, (3) partial connectivity, and (4) no connectivity. Within each treatment plot (10 × 10 m, n = 4 replicates), we measured the abundance and diversity (i.e., alpha and beta) of both flying and ground arthropods using sticky and pitfall traps, respectively. We found that the abundance and diversity of highly mobile flying arthropods were unaffected by habitat connectivity, whereas less mobile ground arthropods were highly impacted. The mean total abundance of ground arthropods was 2.5× and 2× higher in the control and partially connected plots compared to isolated patches, respectively. We also reveal that habitat connectivity affected the trophic interactions of ground arthropods, with predators (e.g., wolf spiders, ground spiders) being highly positively correlated with micro-detritivores (springtails, mites) but not macro-detritivores (millipedes, isopods) as habitat connectivity increased. Together these findings indicate that changes in habitat connectivity can alter the metacommunity structure for less mobile organisms such as ground arthropods. Because of their essential roles in terrestrial ecosystem functioning and services, we recommend that conservationists, restoration practitioners, and land managers include principles of habitat connectivity for ground arthropods when designing biodiversity management programs.

Keywords: arthropods; conservation management; ecological restoration; grasslands; habitat connectivity; metacommunity structure.

FIGURE 1

The relationship between habitat connectivity and individual ground arthropod taxa for 2021. Different letters indicate p < .05 using Tukey's HSD posthoc comparisons. For all boxplots, the top and bottom of the boxes indicate the first and third quartiles, with the center line denoting the median; the whiskers show 1.5 times the interquartile range. The diamond symbols are treatment means for 2021.

FIGURE 2

The effects of grassland connectivity on arthropod composition (i.e., beta diversity) for ground arthropods (a) and flying arthropods (b) in 2021. Ordination bi‐plots show arthropod data based on a Bray–Curtis similarity matrix. Each symbol on the ordination plot represents communities for one of the 16 experimental plots. The length and direction of vector overlays denote the strength of the relationship (Pearson's correlation coefficient with R ² > .55) between the ordination axes and the associated arthropod taxon.

FIGURE 3

The structural equation model showing the effects of habitat connectivity on micro‐detritivores, macro‐detritivores, and predators in 2021. The bolded numbers next to the arrows are standardized coefficients, and the p‐values provide the strength of evidence of a given path. Lastly, the arrow's thickness denotes the strength of the relationship, with the thick arrows representing path coefficients with p < .05.