Uncovering patterns of freshwater positive interactions using meta‐analysis: Identifying the roles of common participants, invasive species and environmental context

Abstract

Positive interactions are sensitive to human activities, necessitating synthetic approaches to elucidate broad patterns and predict future changes if these interactions are altered or lost. General understanding of freshwater positive interactions has been far outpaced by knowledge of these important relationships in terrestrial and marine ecosystems. We conducted a global meta‐analysis to evaluate the magnitude of positive interactions across freshwater habitats. In 340 studies, we found substantial positive effects, with facilitators increasing beneficiaries by, on average, 81% across all taxa and response variables. Mollusks in particular were commonly studied as both facilitators and beneficiaries. Amphibians were one group benefiting the most from positive interactions, yet few studies investigated amphibians. Invasive facilitators had stronger positive effects on beneficiaries than non‐invasive facilitators. We compared positive effects between high‐ and low‐stress conditions and found no difference in the magnitude of benefit in the subset of studies that manipulated stressors. Future areas of research include understudied facilitators and beneficiaries, the stress gradient hypothesis, patterns across space or time and the influence of declining taxa whose elimination would jeopardise fragile positive interaction networks. Freshwater positive interactions occur among a wide range of taxa, influence populations, communities and ecosystem processes and deserve further exploration.

Addressing context dependence in ecology

“…Context dependence is commonly and increasingly invoked in ecology (Appendix S1, Figure S1, and Table S1 in the supplemental information online) [11][12][13][14][15][16][17], as well as in other fields typified by high complexity, large scales, and heavy reliance on observational studies, such as conservation biology [18,19], evolutionary biology [20,21], and epidemiology [22,23]. Context dependence provides a convenient shorthand to describe variation within and between (potentially myriad) studies and is reported across all study types [24][25][26][27][28]. However, because context dependence can result from many processes (as discussed below), unless the underlying causes are identified, concluding that outcomes are context dependent provides little insight by itself.…”

Metapopulation‐level associations in positively interacting stream fishes

“…Positive biotic interactions are recognized as important drivers of species distributions (Holt et al 2002, Afkhami et al 2014, Albertson et al 2021). However, much less is known about the role of positive interactions in driving large-scale distribution patterns (e.g.…”

“…However, much less is known about the role of positive interactions in driving large-scale distribution patterns (e.g. metapopulation) because emerging patterns and consequences of positive interactions have been almost exclusively studied at local scales (Peoples and Frimpong 2016, Arnhold et al 2019, Albertson et al 2021). Here, using a regional fish dataset in the Midwestern US, we unveiled the critical roles of positive interactions in determining the metapopulation-level relationship between hosts and beneficiary stream fishes.…”

“…of Minnesota, St. Paul, MN, USA. competition and predation are well known to influence spatial distributions of the interacting species (Chesson 2000, Ettinger andHilleRisLambers 2013). Additionally, ecologists have begun to recognize the importance of positive interspecific interactions in species distributions (Bruno et al 2003, Afkhami et al 2014, Silknetter et al 2020, Albertson et al 2021. These studies have advanced the field of spatial ecology by pointing to the critical yet overlooked role of positive biotic interactions in predicting species distribution patterns.…”

“…In theory, equilibrium metapopulation occupancy (the proportion of habitat patches occupied within a metapopulation) is ultimately determined by the balance between colonization and extinction of local populations (Moilanen and Hanski 1998, Hanski 1999, Holt et al 2002; therefore, previous empirical studies have made efforts to approximate these critical parameters using key abiotic variables, including habitat size (Franken and Hik 2004), habitat quality (Moilanen and Hanski 1998) and spatial connectivity (Hanski 1999). However, mutualistic and facilitative species should also play a crucial role in mediating the metapopulation-level occupancy of beneficiary species because positive species interactions may influence local colonization and extinction dynamics through improved fitness of beneficiary species (Holt et al 2002, Afkhami et al 2014, Albertson et al 2021. Nevertheless, little is known about how positive species interactions influence the metapopulation occupancy of beneficiary species.…”