Unravelling the effects of multiple types of disturbance on an aquatic plant metacommunity in freshwater lakes
Authors: Lech Jason D. , Willig Michael R. 
Published: May 2021

Lakes and ponds experience numerous forms of disturbance, including land use (anthropogenic), invasive species (biotic), and eutrophication (abiotic). Although these disturbances act independently or synergistically to affect native species composition, their effects generally are not considered simultaneously, thereby failing to account for appreciable variation or inaccurately attributing joint effects to a single type of disturbance.

We assessed defining characteristics (coherence, turnover, and boundary clumping) of a metacommunity of 67 native aquatic macrophyte species that inhabit 104 lakes to determine the extent to which species respond to the same latent environmental gradient and the association of that gradient with multiple interrelated types of disturbance.

Species generally responded to the same latent environmental gradient, with their distributions replacing one another along that gradient, resulting in a compartmentalised structure (i.e. Clementsian pattern). The latent environmental gradient was associated with disturbance; different functional or phylogenetic groups of species were associated with high or low levels of disturbance.

We used variation partitioning to evaluate whether spatial or environmental attributes were more important in driving variation among lakes along the latent environmental gradient. We accounted for 78.7% of variation among lakes in species composition of native aquatic plants, with 10.0% due to unique attributes of space, 16.4% due to unique attributes of environment, and 52.2% due to spatially structured environmental attributes, highlighting the importance of species sorting.

We separated environmental attributes into three subcategories: abiotic (water quality), biotic (invasive species), and anthropogenic (land use). We used variation partitioning on the three environmental subcategories and on spatial attributes to disentangle their independent and joint effects. We then used hierarchical partitioning to unravel the independent and joint effects of each attribute within each subcategory.

Abiotic (water quality), biotic (invasive species), and anthropogenic (land use) disturbances each had significant total effects that are highly conflated with each other. Importantly, each subcategory of disturbance had significant unique effects on native aquatic plant composition.

By using spatial characteristics as well as abiotic, biotic, and anthropogenic attributes that are related to disturbance, we accounted for most of the variability in species composition among lakes. Of particular importance, invasive species independently, and interactively with other environmental characteristics, affected the metacommunity structure of native species. The emergent compartmentalised structure (Clementsian) of native species in the metacommunity arises because of species‐specific differences in response to a disturbance gradient, resulting in species with distinctive functional characteristics and phylogenetic histories at different ends of a disturbance gradient.

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