Lake communities and environmental change

Within-lake habitat heterogeneity mediates community response to warming trends

Evaluating biological responses to climate change at the community level captures diversity in organism response because of differences in life history traits and physiological limits. In addition to biological diversity, habitat heterogeneity can affect fish communities over small spatial scales, even within habitat units that are typically considered relatively homogenous, such as lakes. It is therefore necessary to analyze climate impacts on fish communities while accounting for spatial and temporal patterns in community trends. This project used biological and environmental data from a northern-latitude lake to describe the role of temperature and spatial heterogeneity in predicting changes in community composition. For 50+ years, over which warming effects have been observed in the lake, weekly sampling throughout the summer collected water temperature data and abundance for 14 species captured in the littoral zone. We applied a spatial dynamic factor analysis model to this time series, which estimated sensitivity to changing water temperature for each species and accounts for spatiotemporal variation by describing trends in the community composition for different locations in the lake. This analysis indicated difference in magnitude and direction of species responses to temperature, with some increasing and others decreasing in abundance. Our selected model indicated that different regions in the lake are experiencing different trajectories in community change, associated with differences in rates of temperature change. These results highlight the importance of considering habitat heterogeneity in explaining and predicting future species abundances, and our model provides a means of visualizing spatiotemporal variation in species’ dynamics.

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New work: Zooplankton community response to rapidly changing ice phenology

Northern latitude lakes are undergoing dramatic changes in duration and timing of ice coverage. In addition, some lakes are experiencing years in which open water persists through the winter, and future predictions suggest an increase in these ice-free winters. Ice dynamics directly or indirectly control a range of physical conditions within the lake, including water temperature and stratification, nutrient distributions and water column mixing, physical and biological turbidity, and composition and abundance of bacteria and diatoms. Through these changes in physical conditions and primary production, zooplankton communities are hypothesized to also be susceptible to ice dynamics, but these responses are less straightforward to predict, and depend in part on species composition and life history traits. This project describes the relationship between ice breakup timing, summer temperature, and end-of-summer zooplankton density and community composition for the suite of taxa in Iliamna Lake, Alaska, and tests whether ice-free years fit into an overall warming trend or represent outlier years across a 50 year time series.

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