Isolation controls reestablishment mechanisms and post-drying community structure in an intermittent stream

Area of Science:

• Ecology
• Freshwater Biology
• Conservation Biology

Background:

• Disturbance-prone landscapes host biota with resistance or resilience strategies.
• Habitat fragmentation and isolation can impede recolonization, affecting post-disturbance community recovery.
• Empirical data on isolation's control over community recovery mechanisms are limited.

Purpose of the Study:

• To investigate how isolation (distance from perennial pools) affects invertebrate community recolonization in an intermittent stream after drying.
• To determine the influence of different recolonization pathways (drift, aerial, swimming/crawling, vertical migration) on community reestablishment along an isolation gradient.

Main Methods:

• Monitoring benthic invertebrate reestablishment in Chalone Creek, California, over a ~2-km isolation gradient during rewetting.
• Utilizing mesh traps to differentiate and quantify recolonization via specific pathways.
• Collecting daily emigration samples and surveying benthic communities after 6 weeks.

Main Results:

• Isolation delayed vertical migration from the hyporheic zone.
• Upstream reaches showed higher proportions of resistance strategists, while downstream, more fragmented habitats had increased drift and aerial dispersers.
• Resistance strategists in the hyporheic zone were abundant but largely outmigrated, contributing to downstream resilience.

Conclusions:

• Contrary to conventional views, resistance strategists significantly contribute to both local recovery and downstream resilience.
• Increased isolation reduced invertebrate diversity and increased drought-resistant stonefly abundance.
• Spatial context and the interplay between disturbance and fragmentation are critical for predicting ecosystem recovery and informing conservation strategies.