Oldal 11 [11]
OCR
Foreword | 9 attempt to clarify these differences. The extended discussion about what is and what is not an animal “community” will be of historic interest, as it reflects similar discussions about plant societies that were prevalent at the time. Some of this discussion helps to understand how we arrived at our present community concepts. Regarding the complex terminology, I personally found it to be a barrier to understanding his ideas. For example, he uses the term “semaphoront” to refer to a specific life stage of a species that occurs in a population of interest (“life stage” would have sufficed). A significant logical flaw this work is his assumption that a holistic community concept is real. Whitaker's (1956) very important work on the vegetation of the Smoky Mountains National Park in the US resulted in overthrowing the plant sociology movement and replacing these community concepts with the “individualistic species concept”. This idea is that the populations of each species in a community assemblage reacts individually to the environment and to other species, so that species do not have constant associations with each other. Whitaker’s work suggests that there is no clear way to delineate the boundaries of a plant society, so such “plant societies” do not really exist. Szelényi clearly understands that this boundary problem is central to the identification and reality of an animal “community”, and he devotes a substantial part of this work to address this issue and the related but equally thorny issue of temporal variation and stability. He tries, and in my view, fails to establish spatial boundaries for an animal "community" but in the process recognizes some important issues related to the structure of trophic webs. His approach is to first consider a plant, a single specialist herbivore and the specialized predators (parasites/ parasitoids) associated with the herbivore. He calls each of these catenaria, which we would now call specialized food chains. He then recognizes populations that feed on populations in more than one specialized food chain. These include polyphagous herbivores as well as polyphagous predators. The food webs that are associated with these multiple specialized food chains tied together by polyphagous populations are called presocia. Without the terminology, this is what we now consider to be a food web. What I found interesting is that he divided polyphagous species into large and small ones, with the large ones being vertebrates. These species typically have a much greater home range than the populations of small species, which were mostly arthropoda. The vertebrates link together several of the presocia into spatially larger units, which he called supersocia. Now I believe that the distinctions among these three levels of organization are not clear cut at all, but the idea of considering the scaling of predator size on spatial extent of a food web deserves greater attention. Most of the published food webs are from lakes and ponds, where the spatial extent of the lake or pond create a boundary, but for terrestrial food webs, the issue of spatial scale is paramount and difficult to resolve.
