A community among thistles
Naturalist(s): W.J. Davis and K.A. Finch (photos and video)
Date: Spring 2012
Location(s): Rothenbach Park, Sarasota, FL
Video links below
Field Notes
When walking the trails of Rothenbach Park, I typically hear the songs of a dozen or more birds, spot fish and an occasional alligator in the lake, notice butterflies and bees pollinating flowers, and stumble into the webs of spiders erected across the path. But how many more players, large and small, are hidden from view in the underbrush? To learn more, I devised a plan to videotape all the animals I could find residing in a patch of thistle (Cirsium nuttallii) which grew along one of the paths.
   Overall, I was astounded by the large number of life forms associated with thistles--many too small to capture on video. Furthermore, which species I encountered in the patch varied over time. Butterflies, for example, were most abundant soon after the thistle flowers started blooming, whereas honey and sweat bees always seemed to be present. Once aphids had become established, there was an explosion of Lady Beetles and their larvae. And by the third week various species of spiders had colonized the patch, along with horse flies that presumably harassed passing deer, robber flies that pursued honey bees, and solitary wasps that predated spiders and stink bugs. (Undoubtedly, the webs built by spiders are not only useful in snaring food but provide shelter from their own predators.) I expected to find Cuban Anoles because they are prolific in the park but instead, Karen Finch and I discovered two Green Anoles and a Cuban Tree Frog resting among the prickly leaves.
   For several weeks, Lovebugs were ubiquitous. Without "intentionally" pollinating the flowers or consuming the leaves, the thistle patch apparently provided thousands of Lovebugs with a safe refuge where they could mate. The fact that thistles grow in sunny areas is reason enough for cold-blooded Lovebugs to congregate in the patch where they can bask in the sun.
   I doubt if any of the species I observed are restricted to one type of plant. Like the thistle themselves, most animals visiting the patch have evolved to live a nomadic and/or opportunistic lifestyle, specifically adapted to colonizing disturbed habitat that occurs in open areas. In fact, many thistles in the genus Cirsium are pest species as are the insects that I encountered on them. On this list I would include the Asian Multicolored Lady Beetle and the Eastern Leaf-footed Bug.
   I have had several insights while visiting the thistle patch. First, there apparently exists a large pool of species capable of exploiting a new resource and/or niche–represented in this case by a transitory patch of thistles. Some colonizers will originate from the adjacent forest while others may immigrate over much longer distances (i.e. butterflies). Second, not only does nature abhor a vacuum, but when one species becomes established, its mere presence influences the community's dynamics, often creating (or destroying) opportunities for later arrivals. Third, it does not take long for species to arrange themselves into tropic levels (i.e., a food chain with herbivores hunted by predators etc.) resulting in a functioning, albeit unstable, network or community. And lastly, to capture interesting behavior on video, I will need to spend a considerable more time watching individual species.