SPATIAL DENSITY DEPENDENCE SCALES UP BUT DOES NOT PRODUCE TEMPORAL DENSITY DEPENDENCE IN A REEF FISH

Area of Science:

• Ecology
• Marine Biology
• Population Dynamics

Background:

• Field experiments are crucial for testing ecological hypotheses but often limited by short durations and small spatial scales.
• Extrapolating findings from small-scale experiments to larger spatial domains and predicting temporal population dynamics remains a significant challenge in ecology.

Purpose of the Study:

• To investigate if density dependence observed in small-scale experiments for the goldspot goby (Gnatholepis thompsoni) applies to larger spatial scales and explains temporal population dynamics.
• To assess the effects of intraspecific (conspecifics) and interspecific interactions (bridled goby, Coryphopterus glaucofraenum) on goldspot goby mortality.

Main Methods:

• Conducted density manipulations on small reef patches to assess short-term mortality.
• Correlated initial year-class density with subsequent population decline over five years on five large natural reefs.
• Analyzed spatial density dependence across different reef sizes and temporal density dependence over time.

Main Results:

• Goldspot goby mortality increased with conspecific density in small experimental patches over one month.
• Mortality was spatially density-dependent among reefs for all years, indicating effects scaled up.
• Temporal density dependence was not consistently observed across reefs or years, suggesting limited predictive power for population dynamics.

Conclusions:

• Spatial density dependence in goldspot goby mortality can scale up from small experimental plots to entire reefs.
• Extrapolating findings from small-scale experiments to predict temporal population dynamics is difficult without understanding underlying mechanisms.
• Careful consideration is needed when extrapolating field experiment results to larger spatial domains.