SUBJECT: Species interactions – crucial and usually overlooked part of biodiversity

AUTHOR: Al Vrezec, National Institute of Biology, Ljubljana

SUMMARY: Interactions between species are the main part of biodiversity, although they are rarely present in biodiversity discussions. The author sets out three topics connected to interspecific interactions and biodiversity: (1) interactions in natural communities, (2) interactions with alien species, and (3) interactions of wildlife with human population.

KEYWORDS: interspecific interactions, key species, competition, predation, alien species, apparent competition, interaction with humans, public awareness

Species are the main topic in biodiversity discussion, as we have seen from previous discussions from this conference (see contributions of Alan Feest and Ferdinando Boero), but interactions between them are usually left out from our scope of biodiversity. On the contrary, interactions are one of the main mechanisms that determine species structure in communities and ecosystems, which are number of species and their relative abundances. Here we have to cope with negative interactions (e.g. competition, predation, parasitism), which are better documented in ecological literature, and with positive interactions (e.g. mutualism, commensalism), which are generally less studied and probably underestimated phenomenon. Beside those direct interactions also indirect interactions, e.g. apparent competition, could play very important role in defining which species will survive and which one not. I would like to set out three topics important for understanding the role of interactions in the scope of biodiversity and biodiversity conservation: (1) interactions in natural communities, (2) interactions with alien species, and (3) interactions of wildlife with human population.

Natural communities are structured according to available environmental resources, historical background, and interspecific interactions. In ecological practice, species that have very similar ecological niches, and are therefore in strong negative interactions, e.g. competition, are united in a guild. There are many problems how to determine guild and how to correctly classify right species in the guild. However, our goal in the future should be the identification of guilds, what could be done by increase in knowledge of natural history of species presented in natural communities. Thomas Schoener once pointed three niche dimensions according to which species are segregated: spatial, trophic, and temporal dimension. Those three parameters could therefore be used for such classification. Next step should be identification of key species or competitive dominant species in guilds and communities. I have studied interactions in predator owl guild in montane forests of Slovenia. The guild is composed from three owl species, Ural, Tawny, and Tengmalm’s Owl. The results of the study were that beside negative interactions, e.g. interspecific competition and intraguild predation, also positive interactions have very important role in structuring guilds. According to my study I could presume that certain environmental destruction, e.g. fragmentation of forests, that affect key species, in my case Ural Owl, could have much greater consequences than the other human activities, e.g. selective cutting of wood. Management of natural resources use should be therefore dependent on the vulnerability of key species in the ecosystem.

Alien species able to develop self preserving populations, e.g. invasive species, and other alien species, which are preserved by human interventions, e.g. regular introductions, could be a great threat to the natural communities. These species could compete with native species for resources directly, but indirect effects can be even more effective. As an example is a study about apparent competition between alien Ring-necked Pheasant and native Grey Partridge in Europe. Apparently, the direct competitive interactions are not as strong and destructive as indirect parasite-mediated interactions. Shared nematode parasite is developing in Pheasant much better than in Partridge, but has much greater effect on the later. The marked decline of Grey Partridge in Europe is probably due to this indirect apparent competition also, not only to intensive agriculture. Management of biodiversity conservation in regard to alien species should be pointed in studies of interactions between native and alien species, and in identifying reasons of population decrease of native species. The problem should be addressed also to reintroductions of species in their historical areas. The question is how will reintroduction affect locally established communities?

The last topic is interaction with humans or coexistence of wildlife with human population. In Slovenia this issue was especially set out in connection to large carnivores, e.g. Brown Bear, Wolf, and Lynx, but the problem could be extrapolated also to other for humans “unfavorable” species, for example the Great Cormorant, Raven, Goshawk etc. Large carnivores must be treated as the key species, especially when thinking about their large habitat, waste forest complexes. Conservation of large carnivore’s populations means conservation of their habitat, what is beneficial also for the rest of forest wildlife. The state has very important role in providing the money for recovering damages by large carnivores in agriculture. Another point are threats that large carnivores are presenting to people. In fact, this problem is less common, but very important in facing the problem of large carnivores to the public, especially when regarding reintroductions. People have to learn how to live with large carnivores, and the researchers have to provide persuasive data here. Public awareness is essential!

REFERENCES:
Begon, M., Harper, J.L. and Townsend, C.R. (1996): Ecology – individuals, populations and communities. 3rd ed., Blackwell Science, London.
Bonsall, M.B. and Hassell, M.P. (1997): Apparent competition structures ecological assemblages. Nature 388: 371-373.
Jaksic, F.M. (1981): Abuse and misuse of the term “guild” in ecological studies. Oikos 37: 397-400.
Krystufek, B., Flajsman, B. and Griffiths, H.I. (2003): Living with Bears. A Large European Carnivore in a Shrinking World. Ecological Form of the Liberal Democracy of Slovenia, Ljubljana.
Petty, S.J., Anderson, D.I.K., Davison, M., Little, B., Sherratt, T.N., Thomas, C.J. and Lambin, X. (2003): The decline of Common Kestrels Falco tinnunculus in a forest area of northern England: the role of predation by Northern Goshawks Accipiter gentiles. Ibis 145: 472-483.
Schoener, T. (1974): Resource Partitioning in Ecological Communities. Science 185: 27-39.
Tompkins, D.M., Greenman, J.V., Robertson, P.A. and Hudson, P.J. (2000): The role of shared parasites in the exclusion of wildlife hosts: Heterakis gallinarum in ring-necked pheasant and the grey partridge. Journal of Animal Ecology 69: 829-840.
Vrezec, A. and Tome, D. (in print): Habitat selection and patterns of distribution in a hierarchic forest owl guild. Ornis Fennica 81.