Spider Double Whammy! Jumping Spiders Prefer Vegetated Corridors and Charity for Disabled Wolf Spiders
Spiders are just plain cool. In the recent issue of the Canadian Journal of Zoology, there were two interesting articles on spiders. The photo to the left is of the first paper's study
victimsubject, Phidippus princeps (Photo: Bruce Marlin of Cirrus Images)
Jumping Spiders Prefer Vegetated Corridors
Baker 2007 conducted experiments with jumping spiders, Phidippus princeps (Salticidae), in which he manipulated corridors connecting patches of an old growth field (clover and alfalfa). Patches were either all not connected, all connected, or partly connected by vegetated corridors (as opposed to bare corridors) (see schema below, Fig. 1 from Baker 2007).
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 movement and 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 verts (can we say LAME!). Invertebrates, typically being much smaller, are more subject to small changes and micro-habitat conditions. 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 critters won't risk it out in the open. They need cover to help ensure their survival when moving around. This is a nice arguement for conserving or creating corridors between habitat patches. The next step I think is to link similar principles to biodiversity and ecosystem functioning. Given the same initial starting compositions, do communities differ when habitat patches are linked versus unlinked, or various degrees between?
Charity for Disabled Wolf Spiders
Wrinn & Uetz 2007 studied how leg loss and regeneration affected the condition, growth and development time in the wolf spider, Schizocosa ocreata (Lycosidae). Spiders are able automatize legs as a defense strategy, but it isn't clear what the trade-off is. For instance, if a spider amputates its leg and undergoes regeneration, does that impact future reproduction, make it more susceptible to predation later on, make it less mobile, less of a competitor, or make it harder to find food? Wrinn & Uetz examined the frequency of autonomy in the field and its relationship to size, mass and condition (residuals of the mass to cephalothorax regression, I'll post later about the efficacy of condition indices-something I use in my own research). They also did a laboratory study to test the hypothesis that leg regeneration impairs foraging, decreases growth and/or affects development time.
The field data they collected indicate that reduced foraging ability is associated with leg loss, evidenced by decreases in mass, size and condition. The laboratory experiments also suggest additional trade-offs. Though not significant, spiders regenerating legs took an average of 3.7 days longer to molt. One interesting observation was that
"Although spiders appear to show costs of regeneration, the differences in molt interval, size, and mass between intact and regenerating spiders were only true for the first molt after autonomy. During the second molt after autonomy, regenerating spiders were able to compensate for previous costs by either shortening their molt interval or increasing their growth."It appears that these spiders are pretty flexible and bounce back to minimize costs of loss and regeneration to only one molt. Another trade-off was between development time and mass. Regeneration resulted in either longer time to molt or lower mass, but not both.