Evolution of a stream ecosystem in recently deglaciated terrain

Area of Science:

• Ecology
• Freshwater Biology
• Climate Change Science

Background:

• Climate change drives glacial recession, creating new stream habitats.
• Primary ecological succession is key to understanding community assembly in these new environments.
• Few studies examine community assembly patterns in newly formed stream ecosystems.

Purpose of the Study:

• To investigate the speed and patterns of biotic community colonization and establishment in recently formed streams.
• To compare community assembly in a new stream (Stonefly Creek) with an older, similarly formed stream.
• To identify mechanisms driving community assembly in early-stage riverine ecosystems.

Main Methods:

• Examined species establishment in Stonefly Creek, Alaska, from its emergence (1976-1979) to 2002.
• Utilized stable-isotope analyses to trace nutrient assimilation (e.g., marine-derived nitrogen).
• Compared macroinvertebrate community and biological trait composition with a long-term study of an older stream.

Main Results:

• Stonefly Creek rapidly acquired 57 macroinvertebrate and 27 microcrustacean species by 2002.
• Salmonids colonized within 10 years, followed by other fish species.
• Initially deterministic macroinvertebrate assembly (due to cold temperatures) became more stochastic over time, similar to microcrustaceans.
• Despite low taxonomic similarity (<50%), abundant taxa and functional diversity were similar between streams at comparable developmental stages.
• Marine-derived nutrients from salmon carcasses were assimilated into the food web.

Conclusions:

• Community assembly in new streams can be rapid, initially deterministic, and become more stochastic as conditions change.
• Tolerance appears to be a major mechanism driving community assembly.
• The rapid establishment of diverse communities has significant implications for freshwater biodiversity conservation in warming regions.