Michael Mühlenberg

BIODIVERSITY INDICATOR GROUPS OF TROPICAL LAND-USE SYSTEMS: COMPARING PLANTS, BIRDS, AND INSECTS

Tropical landscapes are dominated by land-use systems, but their contribution to the conservation of biodiversity is largely unknown. Since changes in biodiversity in response to human impact are known to differ widely among taxonomic groups and guilds, there is a need for multidisciplinary collaboration of plant, vertebrate, and invertebrate experts. We used inventories of trees, understory plants, birds (subdivided into endemics, insectivores, frugivores/nectar feeders), butterflies (endemics, fruit feeders), and dung bee- tles in Sulawesi (Indonesia) to characterize a gradient from near-primary to secondary forests, agroforestry systems, and annual crops. As expected, overall species richness tended to decrease within this gradient of increasing habitat modification, but, in contrast to pre- vious studies, we found the species richness between most taxonomic groups to be signif- icantly correlated (36 out of 38 pairwise comparisons). However, on average only 48% of the variance could be explained (within the five main groups), and only a few taxonomic groups/guilds turned out to be good predictors for others: for example, trees for fruit- and nectar-feeding birds (88% explanation) and fruit-feeding butterflies (83%), endemic birds for endemic butterflies (72%), and frugivorous/nectar-feeding birds for fruit-feeding but- terflies (67%). Although biodiversity of land-use systems showed taxonomic group- and guild-specific differences, most groups were affected in a similar way by habitat modifi- cation. Near-primary forest sites proved to be of principal importance for conservation; however, land-use systems such as secondary forests (for understory plants, birds, and butterflies) and agroforestry systems (for butterflies) supported relatively high numbers of species and might play a significant role for biodiversity conservation in tropical landscapes.

The abundance of tree holes and their utilization by hole-nesting birds in a primeval boreal forest of Mongolia

Abstract. The natural tree holes and nest holes of hole-nesting birds were surveyed in four forest types in the west Khentii Mountains of NE Mongolia. The utilization patterns of species, size and condition of trees, as well as hole types, were investigated. The average density of tree holes in the study area approached 30 holes/ha, while that of hole-nesting birds was 2.4 nests/ha only. The riparian mixed forest had the greatest number of species and individuals of hole-nesting birds, while the spruce-fir forest had the lowest numbers. Excavating bird species preferred larger, deciduous trees, and snags. Non-excavators did not select holes according to tree species or size, but preferred holes in living trees and branch holes. In view of the low occupancy of holes among the four habitats, we suggest that the density of secondary hole-nesting birds is not limited by availability of holes in the study area.

Island ecology of arthropods

Summary1.Twenty-five species of web-building spiders (Araneae) were studied by examining standard study areas on 5 islands of the Central Seychelles group that differ in size and degree of isolation. The number of individuals and of species on each island was correlated to the area, altitude, degree of isolation, and resource availability of the respective island. The effect of these factors on niche breadth and niche overlap was also examined.2.In respect to resource availability the structural diversity of each study area was determined by means of the Shannon-Weaver formula. Environmental conditions were broken down into 4 categories according to cover, soil, water, vegetational strata, and number of plant species. In addition to this quantitative method different habitats were defined according to existing plant associations (Table 2). Both methods produced similar results.3.As the islands increased in size, both the spectrum of resources and the number of habitats also increased. Islands of lasrger surface revealed a higher mean as well as a greater range of structural diversity (Fig. 2). Associated with the increased spectrum of resources there was a significant increase of spider species.4.The number S of web-building spider species increases with the size A of the island according to the Wilson formula S=cAz (Fig. 3). The present study revealed the coefficient z to be remarkably low.5.The degree of isolation of an island, calculated according to macArthur and Wilson (1967), did not explain the differing numbers of spider species on the different islands.6.Niche breadth and niche overlap were calculated in terms of numbers of habitats and of ranges of structural diversity. The most abundant spider species had the greatest niche breadth. The average niche breadth became smaller with the increase of island size. Specific niche breadths of spiders on different islands did not vary significantly between islands (Table 6). But in all cases there was a reduced niche overlap in the more diverse spider communities (Tables 5 and 8).7.The total density of the spider community was highest in the structurally most diversified habitats. The total density of web spiders diminished with the decreasing size of the island. The correlation between total density and number of species was significantly positive.8.The low value of the z coefficient in the species-area relationship is discussed. The possibility of a low ecologic saturation on smaller islands is considered. Ways in which species diversity may increase are examined. Analysis of resource availability proved to be more efficient for the solution of ecologic problems than the simple examination of the species-area relationship.

Distribution and status of the hippopotamids in the Ivory Coast

The distribution and relative abundance of the common hippo (Hippopotamus amphibius) and the pygmy hippo (Hexaprotodon liberiensis) was studied in the Ivory Coast between 1978 and 1986 by questionnaire survey, interviews, local field investigations and aerial censuses. In addition, the size of the pygmy hippo population in the Tai Forest area was monitored between 1995 and 2001. At the time of the initial study, the common hippo inhabited the Sassandra, Bandama and Comoé rivers, but was abundant only in the Upper Comoé. The pygmy hippo was restricted to the Guinean Forest zone between 7°25’N (Tiapleu Forest Reserve (Forêts Classée)) in the north and 4°18’W (estuary of the Agnebi River) in the east, where it was abundant in undisturbed rainforest areas. Population data are presented from the Comoé, Tai and Azagny national parks where the ecology of both species was studied in greater detail. The total popu lation of the common hippopotamus was estimated at about 1100 animals in 1978 1984, of which at least 70% concentrated during the dry season in the Upper Comoé, Leraba and Iringou rivers. The average dry season population density in the Comoé varied at that time between three and four animals per river kilometre, in groups of five to six, but had dropped to one to two per kilometre in 2002. During the rainy season hippos disperse upstream into smaller tributaries and downstream as far as the coast. As the forest zone is modified by forestry and agriculture, small herds of common hippos have become resident and in some localities are sympatric with the pygmy hippo. Pygmy hippos are solitary animals, confined to home ranges of 50 150 ha. In optimal habitat their population density can be as high as seven animals/km2, averaging about three animals/km2 over larger areas of undisturbed rainforest. At present, however, hunting pressure has reduced population densities to 0.8 2.5 animals/km2 even in the most favourable ecological conditions of the Tai National Park. Extrapolation of these densities suggests that the total population of pygmy hippos in the Ivory Coast is greater than previously thought, but does not exceed 15 000 animals. Most of these inhabit the Tai National Park and its adjacent protected areas. The remainder occur mainly in various forest reserves (Forêts classées). Ecological factors, which influence population density or limit pop ulation growth of the two different hippo species, are discussed and recommendations made for their conservation.

Predicting Losses of Bird Species from Deforestation in Central Sulawesi

Tropical deforestation and forest fragmentation are probably the most serious threats to biodiversity (see Turner 1996) and it has been theoretically stated that even the largest protected areas in the tropics might be too small to sustain populations of all species of the original system (Terborgh 1999). But species loss in forest fragments is a complex process and appears often only after considerable time lags, especially in vertebrates (Brooks et al. 1999b). Therefore, empirical evidence for such extinctions can only be obtained from areas with a long deforestation history and long-known faunal composition (e.g. van Balen 1999). Such empirical data are scarce but are essential in order to convince land use managers of the long-term effects of forest loss on biodiversity. Species area models, however, are a valuable tool in the prediction of tropical vertebrate species loss (van Balen 1999; Brooks et al. 1997, 1999a, c, 2002; Cowlishaw 1999).

Are There Minimal Areas for Animal Populations

The minimal area of an animal populution is determined by A) the area requirement of reproductive units and B) by the viable population size. A) varies due to individually different and seasonally fluctuating home range sizes and is in addtiion strongly influenced by habitat quality. Population survival depends on deterministic as well as stochastic events and can therefore be estimated only with limited probability. A certain limitation of risk factors can be achieved by enlargement of the population size, increase in number of suitable habitats and reduction of isolation between inhabited areas. To determine the size of a “minimum viable population” (MVP) a “population vulnerability analysis” (PVA) is used as most important data base. The objectives of a MVP (e.g. 95% survival probability for the next 100 years) determines the necessary environmental conditions. A method which allows faster predictions was developed for special demands in practical implementation.

Area Requirement and Isolation: Conservation Concepts and Application in Central Europe

Area has become a precious commodity in densely populated Central Europe and elsewhere. The pressures for multiple land use in most landscapes have led to a steady loss of habitat and to the increasing isolation of habitat remnants. With some exceptions (e.g. species of isolated islands, large game mammals of open landscapes), this process is the most important one for the decline of biodiversity (Henle in press a, Henle & Streit 1990, Wilcove et al. 1986). In spite of numerous activities, the ongoing loss of species could not be stopped.

Studying Species Survival in Fragmented Landscapes: The Approach of the FIFB

The landscapes and ecosystems of Central and Western Europe are of recent origin. They developed after the end of the last ice age. The retreat of the ice was followed by a continuous immigration of species and changes to the developing ecosystems (Erz 1983). Humans played a role in these changes early on by exploiting and cultivating land resources (Ellenberg 1986, Kuster 1992). Natural ecosystems - ecosystems with a minimum of human interference - barely had the chance to evolve or soon disappeared (De Vries 1995).For a considerable time, human land use contributed to a diversification of the developing cultural landscape, made habitats available for many species, and created new ecosystems with a wide range of extensively used habitats. These biotopes, e.g. species rich grasslands, are now considered very valuable for nature conservation because they shrank from about 30% of the cultivated land to less than 1% due to intensification of agriculture and forestry. Even the fauna of our nature reserves principally is now a product of the developing cultural landscape. Within the last century, the cultural landscape rapidly changed again and the diversification process was reversed (Erz 1983). In spite of numerous activities, the on-going decline and finally demise of species could not be stopped. This led to doubts about the efficiency of conservation measures and strategies practiced so far. In Germany, these strategies consisted mainly of the formal protection of numerous small reserves without any consideration of the area required for viable populations and in the implementation of systems of habitats connected by corridors.