Nature Blog Network

Monday, September 3, 2007

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

Photo of a male Schizocosa ocreata from the Uetz lab website.

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.

8 comments:

  1. A few years back, I did a ground spider survey for the Nature Conservancy on one of their properties where they were interested in cataloging the organisms that were living within some rare sand barrens habitat there. Ever being a scientist, I decided to collect from the sand barrens as well as from the surrounding forest. As you might be able to guess from the above study, the overlap in species composition between the two habitats was minimal. Those spiders found in the forest were simply not found in the sand barrens, even though the sand barrens were embedded within the forest matrix.

    After reading about this new study I wonder what a mark-recapture study would reveal about the movement of spiders between sand barren sites within the same forest matrix. hmmm.....

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  2. Thats an interesting question. I would assume the same principles would apply. The sand barrens spiders need resources from that locality that it can't get in the forest, or is being actively excluded from forest by better forest competitors either currently or in the past.

    The whole idea of needing corridors is interesting. It gives hope since humans have decimated so much habitat. If we can conserve existing corridors between protected areas, or create new ones, there is a chance at slowing down local extinction. The key from this study and your comment seems to be to connect like habitats. Can old-growth forest species live successfully in new growth forest or shrub-land? There is a bit of research on looking at the effects of corridors on single species, but I am more interested in preserving biodiversity. If you take a source patch and target patch of equal variables, with the target patch having no animal species, will the species composition of the target patch resemble the source patch when a corridor is opened?

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  3. Some spiders also do something called ballooning. They let themselves be blown away by the wind while being attached to a long silk fiber. Perhaps the jumping spiders don't do that.

    But if they are jumping spiders, why can't they jump across bare strips? HA, HA, HA...

    ReplyDelete
  4. Walt Whitman had a nice poem involving ballooning spiders:

    "A noiseless, patient spider,
    I mark'd where on a little promontory it stood isolated,
    Mark'd how to explore the vacant vast surrounding,
    It launch'd forth filament, filament, filament out of itself:
    Ever unreeling them, ever tirelessly speeding them.
    And you O my soul where you stand,
    Surrounded, detached, in measureless oceans of space.
    Ceaselessly, musing, venturing, throwing, seeking the spheres to connect them.
    Till the bridge you will need be form'd,
    till the ductile anchor hold;
    Till the gossamer thread you fling catch somewhere,
    O my soul."

    Ballooning in spiders is a polyphyletic process. Several different taxa do this, especially juveniles.

    ReplyDelete
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  7. Just watched a thailand garden spider lose a pair of legs about four months ago, during last few days they were regenerated abruptly after molting, about half the size of the other 3 pair. Have pic of one similar, this one is still in my bedroom window, haven't bothered with pictures. If you want to visit my site/email, goto http://foossolvesunified.com

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