Barriers to dispersal come in all shapes and sizes and not all are obvious. Baker conducted experiments with jumping spiders, Phidippus princeps (Salticidae) in which he manipulated corridors connecting patches of old growth fields (clover and alfalfa). Patches were either not connected (bare corridors), all connected, or partly connected by vegetated corridors (see schema below, Fig. 1). Baker found that P. princeps always preferred vegetated corridors and was never found on bare strips.

“The results of this experiment show that corridors are important for the interpatch movement of female P. princeps: spiders moved almost exclusively to patches connected by vegetated strips. In the absence of vegetated strips, spiders rarely moved cross bare substrate to a new habitat even in overcrowded conditions.”

This has pretty fundamental consequences for dispersal ecology. The fact that these spiders will not move across a non-vegetated corridor despite reaching carrying capacity (Baker reports using densities 2-3 times that in nature) underlies the importance of connectivity between habitat patches. This is a ripe area of conservation research, which has mostly been done on large mammals like mountain lions, bears and other endangered vertebrates. Invertebrates, being much smaller, are more subject to small changes and greatly influenced at the micro-habitat level. This study shows how important it is to maintain habitat corridors for the little guys.

“If an animal, as in the case of P. princeps, does not respond to density pressures when habitat patches are surrounded by unfavorable habitat, the persistence of fragmented populations may be severely compromised.”

The fact of the matter is that many critters won’t risk it out in the open. They need cover to help ensure their survival when moving around. This is a nice argument for conserving or creating undisturbed corridors between suitable habitat patches.

Baker, L. (2007). Effect of corridors on the movement behavior of the jumping spider Phidippus princeps (Araneae, Salticidae) Canadian Journal of Zoology, 85 (7), 802-808 DOI: 10.1139/Z07-061