Testing the causal mechanism of the peninsular effect in passerine birds from South Korea

The peninsular effect is a geographical phenomenon that explains patterns of species richness. Given that spatial variation in species richness along a peninsular may be driven by multiple processes, we aimed to identify the sources of latitudinal patterns in passerine species richness and test hypotheses regarding (1) recent deterministic processes (climate, primary productivity, forest area, and habitat diversity), (2) anthropogenic processes (habitat fragmentation), and (3) stochastic processes (migration influence) in the Korean peninsula. We used the distribution data of 147 passerine species from 2006 to 2012. Single regression between passerine species richness and latitude supported the existence of the peninsular effect. Mean temperature increased with decreasing latitude, as did habitat diversity but leaf area index and forest area decline. However, mean temperature and forest area only influenced passerine species richness. Although habitat diversity influenced passerine species richness, it was counter to the expectations associated with peninsular effect. The number of habitat patches decreased as latitude increased but it had no effect on passerine species richness. Ratio of migrant species richness showed no significant relationship with leaf area index, forest area, and habitat diversity. However, the ratio of migrant species richness increased with decreasing mean temperature and that contributed to the increase in passerine species. Overall, our finding indicate that the observed species richness pattern in peninsulas with the tip pointing south (in the northern hemisphere) counter to the global latitudinal gradient. These results were caused by the peninsular effect associated with complex mechanism that interact with climate, habitat area, and migrant species inflow.

Peninsular effect on species richness in Italian small mammals and bats

Peninsular effect is an anomalous gradient in plant and animal species richness from base to tip of a given peninsula. This pattern has been studied intensely on various taxonomic groups, but with scarce attention for using standardized data. Here, using presence-absence data normalized by the field effort, the peninsular effect on the species richness of some mammalian groups (Eulipotyphla [i.e. Soricomorpha + Erinaceomorpha], Rodentia, and Chiroptera) was analyzed along the Italian peninsula. Specifically, species richness at each 30′-wide latitudinal band and the normalized species richness were compared, and generalized linear models (GLM) were used to assess whether habitat diversity, altitudinal range and area of each latitudinal band were the main predictors in explaining the peninsular effects in each of the three mammalian orders. In both Rodentia and Chiroptera, species richness was better predicted by habitat heterogeneity and by the interaction term habitat heterogeneity × field effort. For Eulipotyphla, GLM models gave no significant results. Our study highlighted the importance of taking into account the sampling effort in order to proper evaluate the peninsular effects on species richness in animals.

Distributional patterns of raptors along altitudinal gradients in the northern Andes and effects of forest fragmentation

ABSTRACTA survey of the diurnal raptor community (46 resident species) at five altitudinal levels from 100 to 4600 m was made in Venezuela using 106 1-km2sample quadrats and then compared with similar censuses (211 plots) in southwestern Colombia and eastern Ecuador. Six habitat types were defined and habitat preferences were measured from every encountered birds and from the association between individual abundances and the coverage of habitat types on plots. The overall species richness steeply declined with elevation in all three countries. The raptor community consisted mostly of tropical species that rapidly decreased in both abundance and frequency of occurrence with elevation. A small set of subtropical-temperate forest specialists partly replaced them at mid-elevation and only two species occurred in the paramo of Venezuela, against 5–7 in the other countries. Although originally the gradients were probably almost completely covered with forest, a large part of the raptor community is now composed of grassland species, three of them extending from the lowlands to the tree line. The relative impoverishment of the Venezuelan community, especially at upper levels, is attributed to a peninsular effect at the narrow extreme northern tip of the Andes and perhaps also to former forest fragmentation. Within some species, different subspecies had discrete altitudinal distributions and interspecific competition may explain differences in the range extension of some species between countries. Today, however, accelerating deforestation may result in a severe decline of forest-interior species and a probable reduction in the altitudinal range of at least some of them. Species naturally associated with forest gaps or edges usually tolerate a high degree of forest fragmentation and degradation but only one of them may become abundant in heavily human-altered woodlands. Few grassland specialists have become more widely distributed in the increasingly deforested landscapes.