Dr. Carrel
 
Research Interests:
-- Conservation Biology of Spiders

CONSERVATION BIOLOGY OF SPIDERS

I am in my 18th year of studies of the population ecology of two burrowing wolf spiders and a similar study with the red widow spider, all three of which are considered rare and possibly threatened species. To my knowledge these studies are the only long-term research projects on spiders in the world.  This work is done at the Archbold Biological Station, Lake Placid, FL, a privately owned and operated facility that is situated in one of the most ancient habitats in the world [Florida scrub], which now is recognized as a globally-important hotspot of biological diversity.

I found that the local population of the red widow spider at the Archbold Biological Station shows tremendous long-term fluctuations in densities that might be drive by cyclic variations in attacks by enemies, such as parasitoids [Carrel, J.E. 2001. Population dynamics of the red widow spider (Araneae: Theridiidae). Florida Entomologist 8: 385-390.]. I continue to monitor red widow spider populations every winter.  Now that red widow densities are returning to high levels found in 1988-90, I am starting tests to determine the species identities of enemies that attack the spiders and their eggs/embryos while in the egg sac. 

In addition, I am completing a ms. on an analysis of the diet of the red widow spider based on field data collected in 1990 and 2003.  I collected prey items from the webs of many red widows and Mark Deyrup, the other co-author, identified each insect to species by using his unique knowledge of the insects of Florida.  I did all of the fieldwork, data analysis, and most of the writing.  We found that red widows prefer to eat beetles that themselves are endemic to Florida scrub, suggesting that there may be a strong co-evolutionary relationship between the spider and its prey.  We intend to submit this ms. to the Florida Entomologist in 2005 or 2006.

I have accumulated enough (18) years of data to publish many of the results of my long-term studies of the population ecology of two burrowing wolf spiders that are endemic to Florida scrub.  Two papers came out in 2003 and a third is about ready for submission in the summer of 2005.

The first paper [Carrel, J.E. 2003a. Ecology of two burrowing wolf spiders (Araneae: Lycosidae) syntopic in Florida scrub: burrow/body size relationships and habitat preferences. Journal of the Kansas Entomological Society 76: 16-30.] sets the stage for studies of these spiders  because it validates my field methods.  It also provides regression equations that can be used to estimate reliably the size of spiders based solely on the diameter of the openings to their burrows.  It took me more than a decade to amass these data, but the time was well worth the investment since I showed that interannual variation in my ability to detect spider burrows is small, so my field measures are highly reliable.

 

G. hubbelli, burrowing wolf spider
that makes a turret from leaves around its entrance.
G. hubbelli, burrowing wolf spider

 

The second paper on burrowing wolf spiders [Carrel, J.E. 2003b. Burrowing wolf spiders, Geolycosa spp. (Araneae: Lycosidae): gap specialists in fire-maintained Florida scrub. Journal of the Kansas Entomological Society 76: 557-566.] documents that burrowing wolf spiders prefer gaps in scrub that have open sand, but it also shows that gaps are an ephemeral resource since the native shrubs quickly regenerate after fire. Hence, within one year post-fire there are few suitable sites remaining for spiders to build burrows in.  Hence, in many ways the spiders behave like herbaceous plants, which are known to be endemic, gap specialists in the fire-maintained scrub ecosystem.  For this work I not only had to make replicate measurements of the area of open sand around the burrow entrances of randomly selected spiders, but also I had to determine the size of gaps and the plant species composition at randomly chosen points in many parcels of scrub that were burned at different times [= a chronosequence] in order to assess the dynamics of openings in woody scrub vegetation.


Wildfire in Florida scrub

The third paper is the first long-term study of the population ecology of any spider in the world.  Moreover, for the first time it documents the responses of endemic scrub spiders to two natural 'disasters": fire and flood.  I delayed submitting this ms. in order to incorporate recent (Sept. 2004) data on the effects of hurricane-caused flooding from Hurricane Jeanne, which hit the day I arrived at the Archbold Station and caused flooding of my study sites for the first time in at least 55 years.  Previously I document that both species of burrowing wolf spiders respond positively to burning of the scrub, but within a few years postfire their population densities decline and after more than a decade of fire exclusion they tend to go locally extinct.  These results are based on annual measurements of spider densities in 15 large [10 x 10 m] permanent plots that were burned by wildfires in 1989 and again in 2001.  Furthermore, sampling of the abundance and diversity of insects in recently burned scrub relative to unburned scrub shows that there are fewer prey available after a burn, so increases in spider densities are probably not driven by more prey.  But habitat measures reveal that the exposed soil in burned areas is significantly warmer than in matching unburned scrub for many months postfire, which allows the subterranean spiders to grow and reproduce faster than in unburned scrub and then the many, newly created gaps are colonized by spiders from within and from outside the burned area.  The flooding in the fall of 2004 was followed by a dramatic drop in spider densities as measured in February 2005. But further analyses revealed that plant growth, gap closure, and accumulation of leaf litter also were great, reflecting three years of above average rainfall. Thus, the "presumptive flood effect" on spider densities was confounded by coincidental growth in the shrub matrix.

 

In 2002-2003 I started a new project in the Florida scrub at the Archbold Biological Station dealing with the role of macroarthropods in decomposition of leaf litter.

 

Floridobolus mating
It appears that certain caterpillars as well as the 'rare' scrub-endemic millipede might be the main agents that physically break down the leathery leaves shed by the dominant evergreen shrubs. This work is in collaboration with Mark Deyrup, staff entomologist at the station.  Part of the project, which has become the focus of graduate research by Dani Sattman, deals with the phenology and feeding habits of the Florida scrub millipede.  Even though this millipede is very large and often is locally abundant, nothing is known about it other than a bit about its geographic range. Because the millipede is restricted to a narrow, 100-mile long ridge with scrub in south-central Florida, this species is possibly endangered. By learning more about its natural history, we might better understand its conservation status.


Floridobolus coiled

 

 

 
 
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