Climate change is expected to affect freshwater ecosystems, especially those that are located near a climatically-sensitive ecotone (e.g., treelines). For example, climate warming can promote treeline migrations and reduce glacial cover in mountainous regions, which result in increased catchment vegetation and weathering rates. These climate-catchment interactions can cause alpine treeline lakes to become more chemically concentrated and coloured. Therefore, I used surveys and mesocosm experiments to determine the relative importance of resources and predation to littoral foodwebs in Canadian Rocky Mountain lakes and ponds.

The hypothesis of resource limitation of alpine littoral food webs was tested using a 3-factor experimental design that consisted of two levels of dissolved organic matter (DOM), nutrients (NP), and ultraviolet radiation (UVR). Resource limitation was both habitat- and taxon-specific. Epilithon abundance and community composition were significantly affected by DOM, NP, and DOM-UVR interaction, while epipelon responded to NP and UVR. The responses of phytoplankton and higher trophic levels were marginally significant, or not detected.

The direct and interactive effects of predation and UVR on alpine littoral communities were tested for using a 2-factor experiment. Significant community and population-level responses to UVR were associated with the accessiblity of physical refuges, photoprotective pigmentation, and a high capacity for DNA-repair. Direct predation and indirect UVR effects were not detected despite a 3-fold amendment of consumer biomass.

The results from an altitudinal survey of littoral communities in 20 mountain lakes and ponds corroborated my experimental evidence of the primacy of abiotic regulation of alpine littoral foodwebs. Therefore, my findings suggested that foodwebs in shallow-water alpine ecosystems are very responsive to the effects of climate change, and show a complexity of responses to related changes in the abiotic environment.