Oldal 11 [11]
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.