Refugee Species Research Articles

Summer rainfall variability in European Mediterranean mountains from the sixteenth to the twentieth century reconstructed from tree rings

Since the end of the last glacial period, European Mediterranean mountains have provided shelter for numerous species of Eurosiberian and Boreal origin. Many of these species, surviving at the southern limit of their range in Europe and surrounded by Mediterranean ones, are relatively intolerant to summer drought and are in grave danger of loss, as a result of increasingly long and frequent droughts in this region. This is the case of the Scots pine (Pinus sylvestris) and the Austrian pine (Pinus nigra ssp. salzmannii) which are found on Central Iberian Peninsula at the edge of their natural range. We used a tree ring network of these two species to reconstruct past variations in summer rainfall. The reconstruction, based upon a tree ring composite chronology of the species, dates back to 1570 (adjusted R(2) = 0.49, P < 0.000001) and captures interannual to decadal scale variability in summer precipitation. We studied the spatial representativeness of the rainfall patterns and described the occurrence rate of extremes of this precipitation. To identify associations between macroclimatic factors and tree radial growth, we employed a principal component analysis to calculate the resultant of the relationship between the growth data of both species, using this resultant as a dependent variable of a multiple regression whose independent variables are monthly mean temperature and precipitation from the average records. Spatial correlation patterns between instrumental precipitation datasets for southern Europe and reconstructed values for the 1950-1992 period indicate that the reconstruction captures the regional signal of drought variability in the study region (the origin of this precipitation is convective: thermal low pressure zones induced in the inland northeastern areas of the Iberian Peninsula). There is a clear increase in the recurrence of extreme dry events as from the beginning of twentieth century and an abrupt change to drier conditions. There appears to be a tendency toward recurrent exceptionally dry summers, which could involve a significant change for the Eurosiberian refugee species.

Refugee species: which historic baseline should inform conservation planning?

AbstractUnderstanding species' historical ranges can provide important information for conservation planning in the face of environmental change. Cromsigt et al. (this issue) comment on our recent European bison (Bison bonasus) range reconstruction, suggesting that bison were already 8000 years ago a refugee species (i.e. restricted to marginal habitat due to past human pressure) and that species distribution models (SDM) are generally of limited use for refugee species conservation. While we welcome this discussion, we find no evidence for the claim that human pressure prior to 8000 BP determined where bison occurred. More importantly, as human pressure is generally high and increasing, attempts to restore species across their former range may fail where the factors that relegated species into refugee status are still at play or where their optimal habitat has vanished. Identifying areas where human pressure is low and where refugee species have persisted over the last millennia is crucial, and SDM based on historical data are important for doing so. Refugee species suffer from the shifting baseline syndrome, but careful reality checks are needed and all available data should be considered before determining the baseline that should inform conservation planning.

The difficulty of using species distribution modelling for the conservation of refugee species – the example of European bison

AbstractRefugee species have been confined to suboptimal habitat through historic anthropogenic factors. If this is unknown, management might actively conserve these species in suboptimal habitat assuming it represents optimal habitat. Similarly, species distribution modelling (SDM) might misguide conservation management of refugee species by only using presence data from suboptimal habitats. We illustrate this by commenting on a recentSDMforEuropean bison that reconstructed the historic distribution of the species. We challenge the interpretation of this model by suggesting an alternative historic biogeography based on the refugee species concept. We argue that, in the case of refugee species, historic reconstructions usingSDMcannot be used as a template for conservation management. Rather, experimental re‐introduction programmes should provide us with population performance and life history data from a range of suboptimal to optimal habitats. Such data could be used in mechanistic niche modelling to predict potential distribution of refugee species.

Conservation implications of the refugee species concept and the European bison: king of the forest or refugee in a marginal habitat?

The concept of refugee species provides a theoretical framework towards increasing the predictive power of the ‘declining population paradigm’ through identifying species which are expected to suffer from a declining population syndrome. Using a simple habitat model as a framework, refugee species are defined as those that can no longer access optimal habitat, but are confined to suboptimal habitats, with consequences of decreased fitness and density, and attendant conservation risks. Refugee species may be difficult to detect in the absence of information on prior habitat use and fitness and their observed ecology will be constrained by the habitat limits forced on them. Identification of refugee species, characterisation of pre‐refugee ecology and the restoration of such species to optimal habitat is critical to their successful conservation. The concept is showcased by addressing the conundrum of a large grazing bovid, the European bison Bison bonasus, being managed as a forest specialist, despite its evolutionary background, dental morphology, neonatal behaviour, diet and microhabitat selection being characteristic of a grazing species inhabiting open, grass‐rich habitats. It is hypothesized that a combination of increasing replacement of open steppe by forest cover after the last postglacial period and increasing human pressure forced bison into forests as a refuge habitat. This process was then reinforced through active management of bison in forests as managers committed themselves to the ‘bison as forest species’ paradigm. A research agenda to test this hypothesis using an experimental approach in the conservation management of European bison by introducing populations into diverse habitat types is suggested.

Use of an Exotic Tree Plantation by Bornean Lowland Forest Birds

ABsTRAcr.-During May to July 1982, we surveyed birds in primary forest and in differentaged groves of the exotic tree Albizia falcataria at Sabah Softwoods, a lowland tree plantation in Sabah, East Malaysia (formerly British North Borneo). We found that the Albizia was in general attractive to many native birds. About 60% of primary-forest species used the plantation, and the frequency at which individuals were observed in the oldest groves was almost twice that of nearby primary forest. The Albizia attracted birds because, as an extremely fastgrowing legume with thin leaves, it permitted the rapid development of a well-structured secondary forest. It also was heavily infested with pest insects, which provided an abundant food source. Despite its apparent richness, however, the Albizia lacked several important features of natural forest (e.g. canopy fruits and nest holes). As a result, some primary-forest bird groups were poorly represented (e.g. large canopy frugivores and flycatchers) and others could make only limited use of the plantation (e.g. woodpeckers). In addition, the Albizia is expected to lose its diversity as the plantation as a whole ages. Many of the plantation birds were transients from nearby forest that visited daily to feed, and some probably had been displaced by intense logging. The number of daily transients should decrease as primary forest recedes due to logging and development. Refugee species diversity should suffer from attrition as the plantation is cropped and predation and age take their toll. Received 9 March 1992, accepted 20 November 1992.

On the Diversity of Reptile and Amphibian Species in a Bornean Rain Forest

Intensive collecting carried out over an entire year in 20 square miles of lowland rain forest in Borneo yielded 72 species of amphibians and reptiles considered to be regular inhabitants of the forest floor. Thirty-eight of these species, plus 12 that are "refugees" in the sense that they do not live primarily in this habitat, were collected in 402 quadrats randomly distributed over the forest floor. The average species diversity per individual was H' = 4.26 ± 0.21 bits, using Pielou's (1966a) method for estimating H' and its standard error from individual quadrats. This much diversity is equivalent to 28.3 hypothetical "equilibrium" species having relative abundances distributed according to the "broken stick" model of MacArthur (1957, 1960). The ratio of 28.3 to 84 (72 regular plus 12 refugee species) gives an "equitability" value (Lloyd and Ghelardi, 1964) of E = 0.34. Treating frogs, lizards, and "snakes" separately, we obtain diversity values of 3.30, 3.10, and 2.86 and equitability values of 0.47, 0.67, and 0.28 for the three groups, respectively. Although an equitability of E = 0.34 is well above the "ecological minimum" of E = 0.17 that would characterize 84 species having a lognormal distribution (Preston, 1962), it is surprisingly far below the "ecological maximum" of E = 1.0 that one would expect from the "equilibrium" community of a rain forest-a community rich in species, presumably having relatively constant, equable, predictable conditions for life. This leads us to re-examine the assumption that the rain forest floor environment is relatively constant and predictable. In respect of temperature it certainly is, but not so with rainfall. There is no dry season, but the spacing of heavy rainfalls (more than 1 inch in 24 hr) has an essentially random pattern. Rains of this intensity cause raging floods in the small streams in which many of the frog species breed. Conceivably this might often result in catastrophic mortality. The endless disturbance of intense rains may therefore prevent the community from achieving the theoretical equilibrium. Specimens obtained by general collecting were combined with those caught in the quadrats to form a total forest floor collection for this area of rain forest. Applying Pielou's (1967) method for partitioning diversity by taxonomic hierarchy, only a small part of the total species diversity (0.72 out of 4.65) is attributable to congeneric species living in the same habitat. This holds true also when frogs, lizards, and snakes are considered separately.