Environmental filtering and competitive exclusion drive biodiversity‐invasibility relationships in shallow lake plant communities

Abstract

1. Understanding the processes that influence the diversity of ecological communities and their susceptibility to invasion by exotic species remains a challenge in ecology. In many systems, a positive relationship between the richness of native species and exotic species has been observed at larger spatial (e.g., regional) scales, while a negative pattern has been observed at local (e.g., plot) scales. These patterns are widely attributed to (1) biotic interactions, particularly biotic resistance, limiting invasions in high-diversity locations, producing negative local-scale relationships, and (2) native and exotic richness covarying at larger spatial scales as a function of environmental conditions and heterogeneity, producing positive large-scale relationships. However, alternative processes can produce similar patterns and need to be critically evaluated to make sound inferences about underlying mechanisms.2. We aggregated a large dataset of aquatic vegetation surveys from 1,102 Minnesota shallow lakes collected over 13 years to quantify spatial and temporal patterns of community composition. Using those data and additional information on environmental conditions we evaluated evidence for four distinct mechanisms that could drive patterns of native and exotic species richness: biotic resistance, competitive exclusion, environmental filtering and environmental heterogeneity.3. We found the classic pattern of a negative native-exotic richness relationship at local scales and a positive relationship at lake scales. However, we found no evidence for local-scale biotic resistance; instead, competitive exclusion by invasive species appeared to reduce native species richness after locations became invaded. Evaluating the influence of environmental filtering and heterogeneity, we found that native and exotic species occupied somewhat different niches. Invaders were less sensitive to environmental gradients and more tolerant of a wider range of conditions. This segregation of habitat preferences alone could produce a negative local native-exotic richness relationship and a positive regional pattern without the involvement of biotic interactions. 4. Synthesis. Our findings conflict with established expectations, which come from research predominantly conducted in terrestrial ecosystems. This illustrates the importance of explicitly evaluating underlying mechanisms in diversity-invasibility | 2059 Journal of Ecology MUTHUKRISHNAN eT Al. S U PP O RTI N G I N FO R M ATI O N Additional Supporting Information may be found online in the supporting information tab for this article. How to cite this article: Muthukrishnan R, Hansel-Welch N, Larkin DJ. Environmental filtering and competitive exclusion drive biodiversity-invasibility relationships in shallow lake plant communities.

Invasive species and biotic homogenization in temperate aquatic plant communities

“…However, loss of α-diversity is not the only way invasive species can influence ecosystems (Levine et al, 2003;Vilà et al, 2011). In Minnesota lake-plant communities, invasions did not reduce species richness at the whole-lake scale, although competitive exclusion was previously reported at finer spatial scales (Muthukrishnan et al, 2018). Nonetheless, there appeared to be reorganization of community structure, potentially indicating invaders are driving BH via a broader environmental impact, akin to the effects of urbanization on BH (Blair, 2001).…”

“…Additionally, invasions are frequently associated with habitat degradation or changes in water quality (Didham, Tylianakis, Gemmell, Rand, & Ewers, ; Linde, Izquierdo, Moreira, & Garcia‐Vazquez, ). A number of environmental correlates aligned with anthropogenic impacts (e.g., Secchi depth, chlorophyll a concentrations) are associated with invasion in Minnesota lakes specifically (Muthukrishnan et al, ). Such conditions may promote invasive species as ‘passengers’ of change ( sensu MacDougall & Turkington, ) and are likely to favour common native species that employ a more generalist or environmentally tolerant strategy versus rarer species with narrower environmental niches (Devictor, Julliard, & Jiguet, ).…”

“…Aquatic systems have provided some of the strongest examples of BH (e.g., Olden & Poff, ; Radomski & Goeman, ), yet it is difficult to predict if BH would be a more or less likely consequence of invasions in aquatic versus terrestrial systems. There is some evidence that aquatic plant communities, particularly at higher latitudes, are more strongly controlled by abiotic constraints than terrestrial communities (Muthukrishnan et al, ; Santamaría, ), which would suggest lower ability for aquatic invaders to influence community structure or composition through species interactions. At the same time, because lakes are often distinct spatial units and dispersal between them is limited and highly influenced by human movement (Johnson & Carlton, ), rare species are at greater risk of local extinction, with low potential for rescue, increasing the risk of BH.…”

“…The relationship between invasions and BH could be driven by a variety of mechanisms with different implications for community trajectories and effective management. Invasive species have been shown to competitively exclude native species in these systems (Muthukrishnan et al, 2018), which may disproportionately impact rare and less-competitive species, leading to greater relative abundance of common species. Invasive plant species tend to grow in high-density aggregations, which can potentially change water flow patterns (Cornacchia et al, 2018), nutrient cycling (Geddes, Grancharova, Kelly, Treering, & Tuchman, 2014), or light availability (Urban, Titus, & Zhu, 2009).…”

Niche Models Differentiate Potential Impacts of Two Aquatic Invasive Plant Species on Native Macrophytes

“…Niche-based approaches to address this challenge have a long history in ecology and are an active area of current research [15][16][17][18][19][20][21][22][23][24].In freshwater systems, invasive species are among the strongest drivers of change [25], and invasive aquatic plants cause significant ecological impacts [26,27]. Freshwater lakes are highly susceptible to plant invasions [28,29], and losses of diversity and ecosystem functioning associated with these invasions are of great concern to natural resource managers and other stakeholders [26,30]. Tremendous effort is allocated to preventing and mitigating potential impacts of invasive aquatic plants; better understanding of impacts could be used to improve effort allocation [31][32][33].…”