Global variation in the beta diversity of lake macrophytes is driven by environmental heterogeneity rather than latitude

Abstract

Aim\ud \ud We studied global variation in beta diversity patterns of lake macrophytes using regional data from across the world. Specifically, we examined (1) how beta diversity of aquatic macrophytes is partitioned between species turnover and nestedness within each study region, and (2) which environmental characteristics structure variation in these beta diversity components.\ud Location\ud \ud Global.\ud Methods\ud \ud We used presence–absence data for aquatic macrophytes from 21 regions distributed around the world. We calculated pairwise-site and multiple-site beta diversity among lakes within each region using Sørensen dissimilarity index and partitioned it into turnover and nestedness coefficients. Beta regression was used to correlate the diversity coefficients with regional environmental characteristics.\ud Results\ud \ud Aquatic macrophytes showed different levels of beta diversity within each of the 21 study regions, with species turnover typically accounting for the majority of beta diversity, especially in high-diversity regions. However, nestedness contributed 30–50% of total variation in macrophyte beta diversity in low-diversity regions. The most important environmental factor explaining the three beta diversity coefficients (total, species turnover and nestedness) was elevation range, followed by relative areal extent of freshwater, latitude and water alkalinity range.\ud Main conclusions\ud \ud Our findings show that global patterns in beta diversity of lake macrophytes are caused by species turnover rather than by nestedness. These patterns in beta diversity were driven by natural environmental heterogeneity, notably variability in elevation range (also related to temperature variation) among regions. In addition, a greater range in alkalinity within a region, likely amplified by human activities, was also correlated with increased macrophyte beta diversity. These findings suggest that efforts to conserve aquatic macrophyte diversity should primarily focus on regions with large numbers of lakes that exhibit broad environmental gradients

Lake and catchment‐scale determinants of aquatic vegetation across almost 1,000 lakes and the contrasts between lake types

“…High alkalinity lakes are unquestionably more impacted by anthropogenic pressures than their LA counterparts, being on average 1.2 ecological status classes poorer in the UK based on Water Framework Directive assessments (Willby et al., ). However, the argument that this impact will increase turnover (Alahuhta et al., ) seems unlikely to apply to the HA lakes in our study; greater impact would be expected to increase nestedness relative to other lake types whereas we found the inverse pattern.…”

“…Alahuhta et al. () also noted in their global study that nestedness tended to be highest where overall beta diversity was low. Nestedness in LA lakes might therefore be indicative of their more restrictive growing conditions, whereby less productive/poorly connected lakes of this type only contain a subset of the species pool of the more productive/well‐connected and therefore most species‐rich ones (Bender et al., ; Henriques‐Silva, Lindo, & Peres‐Neto, ).…”

“…β turnover was much higher in HA lakes compared with other lake types (Figure c). Two inter‐related facts could explain this pattern; (a) the larger overall species pool of HA compared to LA lakes (Figure ); (b) HA lakes are more geographically dispersed in Britain (Figure ) than other lake types and environmental heterogeneity, for example in chemistry and substrate, will therefore be correspondingly greater (Alahuhta et al., ). High alkalinity lakes are unquestionably more impacted by anthropogenic pressures than their LA counterparts, being on average 1.2 ecological status classes poorer in the UK based on Water Framework Directive assessments (Willby et al., ).…”

Global patterns in the metacommunity structuring of lake macrophytes: regional variations and driving factors

“…Annual mean air temperature was used as a proxy for thermal energy availability for macrophytes, whereas annual temperature range represented variation in thermal energy availability and its annual distribution in study lakes in different parts of the world (Kosten et al 2009a; Alahuhta et al 2017a). Annual precipitation was not only a surrogate for water-level fluctuation (incl.…”

Environmental drivers of freshwater macrophyte diversity and community composition in calcareous warm‐water rivers of America and Africa

“…Recently, there has been a major effort to improve understanding of the drivers of biogeographical distributions and diversity of freshwater macrophyte species, some (but by no means all) of which have broad planetary distributions (e.g. Alahuhta et al., ; Bornette, Amoros, & Lamouroux, ; Carvalho, Bini, Diniz‐Filho, & Murphy, ; Chappuis, Ballesteros, & Gacia, ; Chappuis, Gacia, & Ballesteros, ; Heikkinen, Leikola, Fronzek, Lampinen, & Toivonen, ; Kennedy et al., , ; Lang & Murphy, ; Makkay, Pick, & Gillespie, ; Morandeira & Kandus, ; Murphy et al., ; Ranieri, Gantes, & Momo, ; Redekop, Hofstra, & Hussner, ; Santamaría, ; Tapia Grimaldo et al., ). Most of these studies have examined macrophyte diversity and distributions in cool‐temperate river and lake systems, with least attention being paid to warm‐water river macrophyte communities.…”