Connectivity of communities interacts with regional heterogeneity in driving species diversity: a mesocosm experiment

Abstract

According to metacommunity theory and previous experiments, inter-patch dispersal rates may alter species diversity at local to regional scales. In this study, we tested the predictions of metacommunity theory regarding the effect of dispersal rates on diversity, with a focus on the impact of environmental heterogeneity. Experiments were conducted in which the dispersal frequencies of freshwater nematode communities and the heterogeneity of local environmental conditions were factorial manipulated by maintaining mesocosms under homogeneous or heterogeneous temperature regime. The effect on biodiversity of the dispersal rate, environmental heterogeneity, and the interaction thereof were evaluated using linear (mixed) models, which showed a significant interaction of the dispersal rate and environmental heterogeneity for alpha-and gamma-diversity measures. Specifically, in homogeneous environments an increase in the dispersal rates led to a decline in diversity at local and regional scales. This was due to the increasing dominance of Daptonema dubium, which was favored by a higher patch connectivity that allowed it to invade local communities. In heterogeneous environments, diversity was unaffected, suggesting that rescue and source-sink effects did not play a role for many species, probably due to the wide temperature range. Diversity was also not impacted by high and low dispersal treatments, and the maximum change was already reached at a dispersal rate of <7% in 4 weeks. The communities were then sampled a second time to investigate the development of diversity when dispersal and thus community connectivity are suspended. After only 12 weeks of isolation, the homogenizing effect of dispersal on community disappeared. The results point to the degree of environmental heterogeneity as key factor in the metacommunity framework. They also demonstrate the need to increase experimental complexity in order to facilitate comparisons between experiments.

Navigating through space and time: A methodological approach to quantify spatiotemporal connectivity using stream flow data as a case study

“…Since many passive dispersers are lost with drying and it takes time for them to recolonise rewetted streams (Bogan & Boersma, 2012;Kappes & Haase, 2012), more perennial sites tend to diverge in their composition as greater species number promotes niche partitioning between habitat patches. In the case of active dispersers, as the spatiotemporal connection between sites increases the communities become more homogeneous due to mass effects (Gansfort et al, 2021;Heino et al, 2015;Sarremejane et al, 2017). Overall, although the study sites were close to each other (mean distance between sites within a stream was around 1 km and all the streams were located within an approximate range of 100 km 2 ), the macroinvertebrate communities showed significant responses to spatiotemporal connectivity.…”

“…Since many passive dispersers are lost with drying and it takes time for them to recolonise rewetted streams (Bogan & Boersma, 2012; Kappes & Haase, 2012), more perennial sites tend to diverge in their composition as greater species number promotes niche partitioning between habitat patches. In the case of active dispersers, as the spatiotemporal connection between sites increases the communities become more homogeneous due to mass effects (Gansfort et al, 2021; Heino et al, 2015; Sarremejane et al, 2017).…”

Detecting patterns of vertebrate biodiversity across the multidimensional urban landscape

“…An interesting highlight of our study is the observed increase in beta diversity despite increase in dispersal, which is plausibly explained by the interactions of heterogeneity, connectivity and contingency. Although higher connectivity maintained by higher forest AI enhances dispersal and may lead to homogenisation under a depleted species pool, social heterogeneity at the metropolitan scale and landscape heterogeneity at the local scale can prevent homogenisation thus averting the decline of beta diversity (Gansfort et al, 2021;Suzuki & Economo, 2021).…”

Soil nematode metacommunities in different land covers: Assessment at the local and regional scales

“…In the freshwater ecosystems, environmental heterogeneity is a key factor of nematode metacommunity as shown in a mesocosm experiment by Gansfort et al. (2021). The dispersal process is another important driver for the metacommunity of passive dispersal nematodes (Ptatscheck et al., 2020).…”