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Open Access Publications from the University of California

About

Frontiers of Biogeography (FoB) is the scientific magazine of the International Biogeography Society (IBS, www.biogeography.org), a not-for-profit organization dedicated to promotion of and public understanding of the biogeographical sciences.  IBS launched FoB to provide an independent forum for biogeographical science, with the academic standards expected of a journal operated by and for an academic society.

Issue cover
Cover Caption: The Central plateau of Terceira Island, with some of the most important fragments of native forest of Azores embedded within a sea of Cryptomeria plantations and pastures. Picture by Paulo A. V. Borges.

Research Articles

Vegetation stability and the habitat associations of the endemic taxa of the Olympic Peninsula, Washington, USA

Explanations for areas of endemism often involve relative climatic stability, or low climate velocity, over time scales ranging from the Pleistocene to the late Cenozoic. Given that many narrowly endemic taxa in forested landscapes display discrete habitat associations, habitat stability should be similarly important for endemic persistence. Furthermore, while past climate variability is exceedingly difficult to quantify on millennial time scales, past distributions of habitats may be robustly inferred from paleoecological records. The Olympic Peninsula, Washington, supports a biota with several insular features including 29 endemic plant and animal taxa. Here I present the geographic distribution and habitat of the endemic taxa, and then examine the vegetation stability of the past 14,300 years from five pollen records associated with discrete vegetation zones on the peninsula. I show that 11 endemics have distributions centered on dry alpine scree and rock in the northeastern quadrant of the peninsula, and nine occur in shaded riparian forests in the southwest. Vegetation turnover during the post-glacial period was smallest in these areas. However, another long pollen record from the western peninsula reveals existence of shrub tundra and greatly reduced forest cover, indicating southward displacement of shaded riparian habitats by perhaps as much as 100 km. Although this study supports an association of post-glacial vegetation stability with endemism, records spanning the glacial maximum indicate widespread tundra during long periods of the late Pleistocene and therefore suggest southern displacement of forest-associated endemics. While some of the alpine scree-associated endemics may have persisted in situ, many others likely arrived via a variety of dispersal trajectories. These histories include dispersal from southern refugia towards ocean barriers preventing further northward dispersal, contraction from more widespread distributions, and recent divergence from sister taxa. This study shows that paleoecological records can cast strong doubt on the inference that areas of endemism necessarily imply in situ glacial survival.

Opinions, Perspectives & Reviews

The mammals of Northern Melanesia: biogeography, systematics and ecology

Northern Melanesia's mammals are poorly known, and perceived deficiencies in faunal records and taxonomic descriptions have, until now, hindered detailed analyses. I examined aspects of biogeography, systematics and ecology in the region's mammalian faunas. Generalized linear models (GLMs) were used to test for differences in rates of persistence in four orders of mammal on continental shelf islands. Ochiai and endemism indices were used to delineate regions of high endemism and influential biogeographic boundaries. A non-parametric multivariate regression tree and GLMs were used to identify the influences of abiotic variables on mammalian species richness. Genetic sequencing, microsatellite genotyping, morphological and ecological data were used to determine evolutionary relationships among the widespread insectivorous bat family, Hipposideridae. Northern Melanesia’s islands support mammalian faunas that reflect the poor over-water dispersal abilities of non-volant mammals; lower rates of long- term persistence in dasyuromorphs and diprotodonts; pronounced diversification of the Family Pteropodidae; and comparative lack of speciation in insectivorous bat families. Analyses produced a clear hierarchical classification of Northern Melanesia’s islands based on their physical attributes and mammal assemblages, providing the first empirical analyses of Northern Melanesia’s and New Guinea’s mammalian zoogeography, and adding to biogeographic theory at both regional and local scales.

 

Analysing and modelling the impact of habitat fragmentation on species diversity: a macroecological perspective

My research aimed to examine a variety of macroecological and biogeographical patterns using a large number of purely habitat island datasets (i.e. isolated patches of natural habitat set within in a matrix of human land uses) sourced from both the literature and my own sampling, with the objective of testing various macroecological and biogeographical patterns. These patterns can be grouped under four broad headings: 1) species–area relationships (SAR), 2) nestedness, 3) species abundance distributions (SADs) and 4) species incidence functions (function of area). Overall, I found that there were few hard macroecological generalities that hold in all cases across habitat island systems. This is because most habitat island systems are highly disturbed environments, with a variety of confounding variables and ‘undesirable’ species (e.g. species associated with human land uses) acting to modulate the patterns of interest. Nonetheless, some clear patterns did emerge. For example, the power model was by the far the best general SAR model for habitat islands. The slope of the island species–area relationship (ISAR) was related to the matrix type surrounding archipelagos, such that habitat island ISARs were shallower than true island ISARs. Significant compositional and functional nestedness was rare in habitat island datasets, although island area was seemingly responsible for what nestedness was observed. Species abundance distribution models were found to provide useful information for conservation in fragmented landscapes, but the presence of undesirable species substantially affected the shape of the SAD. In conclusion, I found that the application of theory derived from the study of true islands, to habitat island systems, is inappropriate as it fails to incorporate factors that are unique to habitat islands.

 

Resources

Compilation of woody species occurring in the Brazilian Atlantic Forest complex

The Atlantic Forest is a hotspot for biodiversity conservation because of its high levels of endemism and threatened areas. Three main forest types, differentiated by their floras, compose the Atlantic Forest: ‘Atlantic Forest’ sensu strictu, ‘Araucaria Mixed Forest’ and ‘Seasonal Forest’. The flora comprises taxa from the Amazon forest, Cerrado gallery forests and the Andean region, which makes the Atlantic Forest a relevant study system for ecologists and biogeographers. Here, we present data from 206 floris- tic checklists describing the occurrence of 1,916 species across the southern portion of the Atlantic Forest. This dataset can be useful for understanding mechanisms underlying plant community assembly processes and the historical relationships between different forest formations.

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Cover

The Central plateau of Terceira Island

The Central plateau of Terceira Island, with some of the most important fragments of native forest of Azores embedded within a sea of Cryptomeria plantations and pastures. Picture by Paulo A. V. Borges.