Invertebrate Metacommunity Structure and Dynamics in an Andean Glacial Stream Network Facing Climate Change

Abstract

Under the ongoing climate change, understanding the mechanisms structuring the spatial distribution of aquatic species in glacial stream networks is of critical importance to predict the response of aquatic biodiversity in the face of glacier melting. In this study, we propose to use metacommunity theory as a conceptual framework to better understand how river network structure influences the spatial organization of aquatic communities in glacierized catchments. At 51 stream sites in an Andean glacierized catchment (Ecuador), we sampled benthic macroinvertebrates, measured physico-chemical and food resource conditions, and calculated geographical, altitudinal and glaciality distances among all sites. Using partial redundancy analysis, we partitioned community variation to evaluate the relative strength of environmental conditions (e.g., glaciality, food resource) vs. spatial processes (e.g., overland, watercourse, and downstream directional dispersal) in organizing the aquatic metacommunity. Results revealed that both environmental and spatial variables significantly explained community variation among sites. Among all environmental variables, the glacial influence component best explained community variation. Overland spatial variables based on geographical and altitudinal distances significantly affected community variation. Watercourse spatial variables based on glaciality distances had a unique significant effect on community variation. Within alpine catchment, glacial meltwater affects macroinvertebrate metacommunity structure in many ways. Indeed, the harsh environmental conditions characterizing glacial influence not only constitute the primary environmental filter but also, limit water-borne macroinvertebrate dispersal. Therefore, glacier runoff acts as an aquatic dispersal barrier, isolating species in headwater streams, and preventing non-adapted species to colonize throughout the entire stream network. Under a scenario of glacier runoff decrease, we expect a reduction in both environmental filtering and dispersal limitation, inducing a taxonomic homogenization of the aquatic fauna in glacierized catchments as well as the extinction of specialized species in headwater groundwater and glacier-fed streams, and consequently an irreversible reduction in regional diversity.

Metacommunity structuring in Himalayan streams over large elevational gradients: the role of dispersal routes and niche characteristics

“…The lack of importance of river network distance may have been somewhat due to glacial runoff effects on instream conditions along the dispersal network, although there was no evidence that this differed between the catchments. Glacial runoff can alter the water chemistry, creating unfavourable conditions for certain taxa, thereby acting as a dispersal barrier for instream dispersers (Cauvy‐Fraunié et al ., ). Results on the most important dispersal routes for stream metacommunities inhabiting dendritic networks have been equivocal (Landeiro et al ., ; Grönroos et al ., ; Cañedo‐Arguelles et al ., ; Kärnä et al ., ), but this, of course, depends on the environmental context.…”

Rapid decline of snow and ice in the tropical Andes – Impacts, uncertainties and challenges ahead

“…Glacial meltwater contribution to these systems is a main driver of spatio-temporal biodiversity patterns, species composition of natural plant and animal communities, as well as key ecosystem processes such as primary production. For instance, glacier-fed streams contribute to environmental heterogeneity in river networks at the catchment level, promoting regional biodiversity (Jacobsen et al, 2012;Cauvy-Fraunié et al, 2015;Quenta et al, 2016). Jacobsen et al (2012) first pointed out that highly specialized communities exist in Andean glacier-fed rivers.…”

“…The effect of changes in species composition are therefore difficult to predict, as are potential altitudinal range shifts in response to changes in in-stream environmental conditions due to reduction in glacial cover in the catchment . As demonstrated by Cauvy-Fraunié et al (2015), the glacial meltwater provides for a spatial filter, essentially insulating the highly adapted species from competition from other more common generalist species unable to cope with the harsh environmental conditions in glacier-fed rivers, and thus excluded from dispersing upstream. With a reduction in glacial meltwater this environmental filter will weaken or eventually completely disappear, allowing colonization through more competitive species from further downstream leading to the possible extinction of these highly adapted endemic 'glacial' species.…”

Egg development and hatching success in alpine chironomids

“…Recent publications have faced this problem, which has led to a significant increase in knowledge regarding the causal connection between key abiotic conditions and alpine chironomids (Brown et al., ; Burgmer et al., ; Cauvy‐Fraunie, Espinosa, Andino, Jacobsen, & Dangles, ; Füreder, ; Füreder, Schütz, Wallinger, & Burger, ). Based on the models proposed by Milner and Petts () and Milner, Brittain, Castella, and Petts (), Rossaro, Lencioni, Boggero, and Marziali (), Marziali and Rossaro (), and Niedrist and Füreder () defined species‐specific ranges of temperature for their occurrence, underlining the significance of water temperature for the dispersal of chironomid larvae.…”