The relationship between body size (M) and abundance (N) is a well-documented allometric scaling relationship and links traits of individual species to the structure of whole ecological communities. In general M-N relationships are negative and linear, however despite this, M-N slopes vary within and between particular ecosystem types for reasons not fully understood. Environmental perturbations or the introduction of nonnative species, may affect M-N relationships as they often have a greater influence on larger species. Consequently, M-N relationships constructed from snapshot data may provide relatively easy-to-quantify, time-integrated, measures of community stability. To determine what conditions cause M-N relationships in streams to depart from consistent patterns, I analysed M-N data collected from a wide range of stream communities in New Zealand. The 25 streams sampled, varied in their disturbance regime, their size and range of top fish predators.
Results/Conclusions
Results from the above analysis showed that M-N relationships varied across streams and departed from the null expectation in many cases. These departures were significantly related to habitat size but not physical disturbance. Larger streams had significantly steeper M-N relationships compared to smaller streams and showed M-N relationships most closely related to the null expectation of -1. Steeper relationships in larger streams were partially driven by the ability of larger streams to support a greater maximum predator mass and a more diverse range of fish predators. Consequently, these results indicate the potential strong influence of habitat size on food web stability. These results also illustrate how body size data can increase our understanding of biotic and abiotic factors influencing the structure and dynamics of ecological communities.