The dynamic matrix predicts population response to long-term experimental forest fragmentation

Context

Earth's forests are fragmented. Species' long-term persistence depends on their conservation in fragmented landscapes with remnants embedded in a matrix of human land use. This matrix influences species' persistence in fragments by determining their degree of isolation and the extent to which edge effects alter habitat. Matrix habitat is often dynamic, so its impact on persistence of remnant species changes over time.

Objectives

Previous research showed that the abundance response of predatory beetle species to matrix habitat predicted their response in fragments with a log-response ratio of about 0.5. When abundance declined in the matrix, there was a smaller but predictable decline in fragments. However, the predictive utility of a fragment:matrix log-response ratio needs testing with functionally different species, more detailed data, and a focus on mechanism.

Methods

In the Wog Wog habitat fragmentation experiment, we follow a detritivorous amphipod 27 years after forest fragmentation.

Results

The amphipod's response in habitat fragments was predicted by its response in the matrix with a log-response ratio of about 0.5, similar to predatory beetles. The amphipod's response was explained by its abiotic niche. The amphipod's short-term response did not predict its long-term response.

Conclusions

The log-response ratio might generalize across the invertebrate food web. For two groups within the Wog Wog experiment, a species' dynamic response in matrix habitat predicted its persistence in fragments. Future work should explore the generality of this finding. With knowledge of projected land use of matrix habitat, a species' matrix response could be used for management planning.
Methods
Invertebrates were sampled four times per year from 1985 to 1998, once during each season, November (spring), February (summer), May (autumn), and June (winter), and three times per year from 2009 to 2014 (each season excluding winter). Pitfall traps were opened for seven days during each sampling period. Traps were 8.5 cm diameter, 475 ml plastic cups filled with a 150 ml solution of 75% ethanol (95%), and 25% glycol. Samples for the two traps at each monitoring site were pooled. Amphipods were identified and counted in the laboratory.