4.4.5 — Geographic threat analysis

The ecological effects of the growth in human population, and of its economic growth, lead to numerous conflicts with "wildlife", mostly summarised as "habitat destruction". From a conservationist's point of view, the consequence is to protect "wilderness" effectively by isolating it as well as possible from human impact. However, this strategy is unrealistic for most parts of the world, except some remote "wilderness areas". As a result, a number of conservationists are now trying to "concentrate" their efforts on certain "hotspots" (geographically) or certain groups of organisms, to "maximise" conservation under the pressure of limited resources. As outlined above, such a limitation will not be appropriate to save migratory species, which often have vast ranges, or aggregate outside the priority areas of conservationists.

Threats to species or species assemblages can obviously be inferred or even predicted from an analysis of habitat destruction. This is exemplified by the estimates of species extinctions based on species-area relationships (Simberloff 1984). Based on annual rates of tropical rainforest destruction of 0.7 percent, and a conservative estimate of 5 million species worldwide, Wilson (1988) calculated the staggering number of 17,500 species becoming extinct per year. In spite of the uncertainties of this calculation, which is based on the assumption that half of the (undescribed) rainforest species are highly localised endemics, the overall conclusion holds that "[...] both the per-species rate and absolute loss of number of species [...] would be about 1,000 to 10,000 times that before human intervention" (l.c. p. 13).

The frightening numbers of possible extinctions mainly refer to insects and other invertebrates, most of which are undescribed and will never appear on any Red List. But in essence, the same methodology can be applied for vertebrates. A quick look at the geographical distribution of extinct taxa, as listed by the IUCN Red List 2000, shows in fact that the number is highest for tropical islands with a high degree of endemism. With 250 extinct taxa, the United States leads ahead of French Polynesia (64) and Mauritius (50) (cf. Hilton-Taylor 2000, Figure 11). Within the United States, most extinctions have been reported for Hawaii. A similar picture emerges for extinct birds, most of which are insular endemics (Table 4.1). In contrast, comparatively few migratory bird species have gone extinct, which could be explained by the huge areas (still) occupied by most species. Seabirds, however, are in an intermediate situation, because their breeding ranges are confined to highly localised and often insular nesting colonies (Figures A2.54-A2.57). This explains the high number of threatened migratory seabirds. Other migratory species were once widespread, but have suffered a considerable range contraction, such as cranes (Figures A.41-A2.46) or the blue swallow (Hirundo atrocaerulea: Figure A2.70). This brings these species into a situation similar to that of endemic species, making them extremely vulnerable to habitat destruction or stochastic events.

The IUCN Red List (Hilton-Taylor 2000) documents local extinctions of endangered species on a country level. This permits calculation of the numbers of locally extinct migrants per country. The result as shown in Table 4.15 differs completely from Table 4.14: the species concerned were formerly widely distributed, but have now gone extinct in several larger range states. Other widespread species, such as Palaearctic songbirds, suffer from local extinctions which did not reduce world populations enough to bring these species onto the International Red List. Some of these extinctions are documented by the national Red Lists of the respective countries. Note that the picture shown in Table 4.15 would look much worse if national Red List Data were evaluated in the same way! The wryneck (Jynx torquilla) and the lesser grey shrike (Larius minor) are already extinct in several European countries (Netherlands, Germany, Austria, Great Britain). Such local extinctions point to serious threats within the respective countries, which sooner or later will affect other, less sensitive species.

For many species, habitat conversion, degradation and loss are the most important threats. The rise of agriculture resulted in a severe modification of habitat, starting early in history with the rise of civilisations — examples include the destruction of Egyptian wetlands and the drying up of the Tiber swamps. But many species adapted, and even thrived, within the landscapes modified by man. Particularly in Europe, practically all surviving migratory birds have adapted to anthropogenically modified habitat (Gatter 2000). Some of them are excellent examples of sustainable agriculture where man and animals have found a stable balance. These systems have existed for centuries, and probably could continue "forever" (i.e. sustainably). Today, they are threatened by modern, more intensive agricultural practices throughout the world. Other habitats such as forests or peat swamps are damaged by direct exploitation. Finally, human activities result in a broad array of detrimental indirect effects upon all kinds of habitats. Such activities include road construction and land sealing, industrial development, water use, tourism and energy consumption. The latter results in climate change, which might be the least predictable, but most severe and irreversible threat to a wide variety of ecosystems.

It is evident that GIS techniques can be of great use to predict the effect of habitat threat on species. The many possible applications are far beyond the scope of this analysis, but it is hoped that GROMS will facilitate and stimulate "predictive threat analysis". This is necessary to overcome the "hind-sightedness" of many conservation plans, which often start when species are already on the brink of extinction. The geographic approach is particularly important for migratory species, as many of them cover huge ranges, and use distinct habitats during their journeys.

This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species ­ Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD

 by Klaus Riede