Identifying temporal and spatial patterns of diatom community change in the tropical Andes over the last c. 150 years

Abstract

Aim Lakes in the Ecuadorean Andes span different altitudinal and climatic regions, from inter Andean plateau to the high‐elevation páramo, which differ in their historical evolution in the several centuries since the pioneering Humboldt expeditions. Here, we evaluate temporal and spatial patterns of change in diatom assemblages between historical (palaeolimnological) and modern times. Location Ecuadorean Andes Methods We compared historical (pre‐1850) and modern (2017) diatom assemblages from 21 lakes and determined the relative role of environmental (water chemistry and climate) and spatial factors (distance‐based Moran's eigenvectors maps) on both assemblages using non‐metric multidimensional scaling (NMDS) with environmental fitting. In addition, we used redundancy analysis (RDA) with variance partitioning to estimate the historical (measured using downcore assemblage composition) effects on modern diatom assemblages and identified diatom species that contributed most to dissimilarity between the two times. Results Diatom changes between the two time points were limited across the group of lakes, as indicated by the NMDS ordination. Variance partitioning indicated that modern diatom assemblages were affected by environmental and spatial effects, but with non‐significant effects of past diatom species composition. Ordination results showed that variables related to elevation and water chemistry affected both modern and historical diatom assemblages. Diatom species with the best fit on NMDS axes (i.e. >70%) were influenced by elevation and climatic variables. The most distinctive change between the two time periods was the higher relative abundance of planktic diatom species in top‐core assemblages of some lakes, but in a highly variable fashion across gradients of increased elevation and water depth. Main conclusions Landscape palaeolimnological analyses of varied Ecuadorean Andean lakes demonstrate both environmental and spatial controls on diatom metacommunities. The multi‐faceted ecological control of the altitudinal gradient on both historic and contemporary diatom assemblages suggests species sorting and dispersal constraints operating at centennial time‐scale. Although a few individual lakes show substantive change between the 1850s and today, the majority of lakes do not, and the analysis suggests the resilience of lakes at a regional scale. We emphasize the potential of diatom palaeolimnological approaches in biogeography to test ecologically relevant hypotheses of the mechanisms driving recent limnological change in high‐elevation tropical lakes.

Ecological resilience in tropical Andean lakes: A paleolimnological perspective

“…In the Ecuadorian páramo, shallow lakes (< 8 m depth), such as Fondococha, are strongly influenced by energy transfer from the catchment (e.g., organic matter, floods, land use) (Giles et al 2018), whereas deeper lakes (e.g., Piñan, albeit cored in the shallow platform) respond more to local physical and chemical conditions in the water column (e.g., nutrients, thermal stratification) (Luethje 2020). We confirmed that Andean lake diatom communities are influenced by both local and regional factors (in agreement with Benito et al 2019); thus, the observed asynchrony is likely due to water chemistry differences mediated by lake‐specific flushing (Leavitt et al 2009).…”

Water chemistry variation in tropical high‐mountain lakes on old volcanic bedrocks

“…The Cajas alkalinity range includes the two ecological thresholds (i.e., $ 200 and $ 1000 μeq L À1 ) identified in European mountain ranges in terms of community composition (Catalan et al 2009a). Diatoms and some crustaceans show this nonlinear community response to the alkalinity gradient, which will be interesting to confirm in this far-flung lake district, which shares with European ranges many diatom species (Benito et al 2019), but not crustaceans (Catalan and Donato-Rond on 2016).…”

“…Currently, high‐mountain lakes across the globe are considered sentinels of the systemic change of the planet (Moser et al 2019). In this context, there is a growing interest in tropical high‐mountain lakes (Michelutti et al 2015; Van Colen et al 2017; Benito et al 2019; Steinitz‐Kannan et al 2020; Zapata et al 2021), which have historically received less attention (Eggermont et al 2007). Although high‐mountain lakes are among the most comparable ecosystems globally, and a common conceptual framework might be used to analyze them (Catalan and Donato‐Rondón 2016), tropical high‐mountain lake regions have unique environmental characteristics that require special attention.…”

Spatial and Temporal Ecological Uniqueness of Andean Diatom Communities Are Correlated With Climate, Geodiversity and Long-Term Limnological Change

“…Biological assemblages accumulate with lake sediments as natural archives, which can be used to understand temporal dynamics of biodiversity and provide insights into the organization of ecological communities and their responses to natural and human-induced drivers (e.g., habitat loss, human impacts, eutrophication) (Willis et al, 2010;Heino et al, 2016). Because lakes are not isolated in the landscape (rather they form a continuum embedded in a terrestrial matrix), researchers have also examined the role of spatial variables in determining biodiversity patterns using paleolimnological approaches (Castillo-Escrivà et al, 2017;Benito et al, 2019). However, contemporary and paleolimnological studies still remain largely disconnected in biodiversity and environmental change research (Gregory-Eaves and Beisner, 2011).…”