Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

The cancer stem cell (CSC) hypothesis suggests that neoplastic clones are maintained exclusively by a rare fraction of cells with stem cell properties. Although the existence of CSCs in human leukaemia is established, little evidence exists for CSCs in solid tumours, except for breast cancer. Recently, we prospectively isolated a CD133+ cell subpopulation from human brain tumours that exhibited stem cell properties in vitro. However, the true measures of CSCs are their capacity for self renewal and exact recapitulation of the original tumour. Here we report the development of a xenograft assay that identified human brain tumour initiating cells that initiate tumours in vivo. Only the CD133+ brain tumour fraction contains cells that are capable of tumour initiation in NOD-SCID (non-obese diabetic, severe combined immunodeficient) mouse brains. Injection of as few as 100 CD133+ cells produced a tumour that could be serially transplanted and was a phenocopy of the patient's original tumour, whereas injection of 10(5) CD133- cells engrafted but did not cause a tumour. Thus, the identification of brain tumour initiating cells provides insights into human brain tumour pathogenesis, giving strong support for the CSC hypothesis as the basis for many solid tumours, and establishes a previously unidentified cellular target for more effective cancer therapies.

Identification of human brain tumour initiating cells

Human alteration of the global environment has triggered the sixth major extinction event in the history of life and caused widespread changes in the global distribution of organisms. These changes in biodiversity alter ecosystem processes and change the resilience of ecosystems to environmental change. This has profound consequences for services that humans derive from ecosystems. The large ecological and societal consequences of changing biodiversity should be minimized to preserve options for future solutions to global environmental problems.

Consequences of changing biodiversity

Modern climate change is producing poleward range shifts of numerous taxa, communities and ecosystems worldwide. The response of species to changing environments is likely to be determined largely by population responses at range margins. In contrast to the expanding edge, the low-latitude limit (rear edge) of species ranges remains understudied, and the critical importance of rear edge populations as long-term stores of species' genetic diversity and foci of speciation has been little acknowledged. We review recent findings from the fossil record, phylogeography and ecology to illustrate that rear edge populations are often disproportionately important for the survival and evolution of biota. Their ecological features, dynamics and conservation requirements differ from those of populations in other parts of the range, and some commonly recommended conservation practices might therefore be of little use or even counterproductive for rear edge populations.

/pdf/conserving-biodiversity-under-climate-change-the-rear-edge-5fy46kgm1e.pdf

Conserving biodiversity under climate change: the rear edge matters.

Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our understanding of the causes of range limits.

https://faculty.ucmerced.edu/sites/default/files/jasonsexton.com/files/sexton_2009_annualreviewofecologyevolutionandsystematics.pdf

Evolution and Ecology of Species Range Limits

As one moves from the core to the periphery of a species' geographical range, populations occupy less favourable habitats and exhibit lower and more variable densities. Populations along the periphery of the range tend to be more fragmented and, as a result, are less likely to receive immigrants from other populations. A population's probability of extinction is directly correlated with its variability and inversely correlated with density and immigration rate. This has led to the prediction that, when a species becomes endangered, its geographical range should contract inwards, with the core populations persisting until the final stages of decline. Convinced by these logical but untested deductions, conservation biologists and wildlife managers have been instructed to avoid the range periphery when planning conservation strategies or allocating resources for endangered species. We have analysed range contraction in 245 species from a broad range of taxonomic groups and geographical regions. Here we report that observed patterns of range contraction do not support the above predictions and that most species examined persist in the periphery of their historical geographical ranges.

Dynamic biogeography and conservation of endangered species

Aim We examined the range contraction of 309 declining species of animals and plants to determine if the contraction dynamics better matched predictions based on the demographic characteristics of historical populations (demographic hypothesis) or based on the contagion-like spread of extinction forces (contagion hypothesis).



Location Species included in the analysis came from all biogeographic regions.



Methods We obtained range maps for 309 species from literature or through personal correspondence with authorities. Hypotheses were contrasted by examining the sequence of changes in the proportion (C) of the remnant range that fell within the central region of the historical range. Monte Carlo simulations and polynomial regressions were employed to examine changes in C during the process of range contraction.



Results The results of the Monte Carlo simulations indicated that more species had observed range contractions consistent with the contagion hypothesis than expected by chance (z-score = 2.922, P = 0.002). The Monte Carlo analysis also indicated that the number of species whose observed range contractions were consistent with the demographic hypothesis was no greater than expected by chance (z-score = 0.337, P = 0.367). The results of the polynomial regression analysis for the two most common taxonomic groups (mammals and birds) and for all geographical regions (Australia, Africa, Eurasia, and North America) we examined also supported the contagion hypothesis.



Main conclusions Most of the examined range contractions are consistent with the contagion hypothesis and that the most likely contagion is human related disturbance. These results have important implications for the conservation of endangered species.

Trajectories to extinction: spatial dynamics of the contraction of geographical ranges

Population densities of terrestrial animals tend to be higher and less variable near the center versus along the periphery of a species' geographic range. If extinctions are tied to local population dynamics, geographic ranges of endangered species should collapse inward, with remnant populations persisting near the center of a species' historic range. Geographic-Information-System analysis of range collapse in nonvolant, terrestrial mammals reveals, however, that extant populations of 23 of 31 species were located along the periphery, not the center, of their historic range. In addition, range collapse appears to be independent of fragment area and has a directional bias from east to west. Persistence of endangered populations also appears to be greater on islands than on continents. These results contradict conventional wisdom in biogeography and macroecology and have important implications for conserving biodiversity. Because of their relative isolation from central populations and from a suite of anthropogenic disturbances, islands and other sites along the periphery of a species' historic range represent critical refugia for many endangered species.

Splendid Isolation: Patterns of Geographic Range Collapse in Endangered Mammals

Various grassland bird species have displayed population declines over the past 30 to 40 years, and interest in explaining possible causes for the declines has prompted numerous studies. Many of these studies have focused on changes in agricultural practices; few have evaluated possible effects of the presence of nonnative grasses in grasslands. The objective of our study was to determine the effects a nonnative grass, Old World bluestem (OWB; Bothriochloa ischaemum), might have on grassland bird species abundance and richness, and on bird food availability (arthropod biomass). Three pastures each of native range, expired Conservation Reserve Program (CRP), and OWB were sampled from May to July 2001 in Comanche County, Kansas. Bird abundance and species richness were assessed by using a point-count method along 3 transects in each pasture. Food availability was estimated by collecting arthropods along 10 transects in each pasture by sweep-netting. Results showed significantly lower bird abundance...

https://bioone.org/journals/The-Southwestern-Naturalist/volume-51/issue-4/0038-4909(2006)51[524:EOOWBB]2.0.CO;2/EFFECTS-OF-OLD-WORLD-BLUESTEM-BOTHRIOCHLOA-ISCHAEMUM-ON-FOOD-AVAILABILITY/10.1894/0038-4909(2006)51[524:EOOWBB]2.0.CO;2.pdf

Effects of old world bluestem (bothriochloa ischaemum) on food availability and avian community composition within the mixed-grass prairie

Old World Bluestems (OWB), introduced from Europe and Asia in the 1920s, recently have begun to raise concerns in the Great Plains. Despite suggestion in the late 1950s that OWB were weedy and negatively impacted biological diversity, they were widely introduced throughout the Great Plains for agricultural purposes. Anecdotal evidence suggests that OWB exhibit invasive characteristics that promote competitive exclusion of native species. The objective of our study was to quantify the competitive abilities of two OWB species (Caucasian bluestem; Bothriochloa bladhii (Retz.) S.T. Blake (= Bothriochloa caucasica (Trin.) C.E. Hubb.) and yellow bluestem; Bothriochloa ischaemum (L.) Keng) with three native grass species (big bluestem (Andropogon gerardii Vitman), little bluestem (Schizachyrium scoparium (Michx.) Nash), and sideoats grama (Bouteloua curtipendula (Michx.) Torr.)). A greenhouse target-neighbor study was conducted to assess both interspecific and intraspecific competition. A total of 480 pots (4.4 l) filled with native soil was used with all pair-wise combinations of species and four density treatments (six replications). Vegetative tiller height, above- and belowground biomass were measured at the end of 16 weeks. Both of the OWB significantly inhibited at least one growth parameter of the three native grass species, while most of the native species did not inhibit growth of either OWB species. Growth of B. ischaemum was enhanced when grown in association with S. scoparium. Based upon the results of our study of OWB competitive superiority and previous research, many of the characteristics possessed by OWB are found to be in common with known invasive species. Hence, we propose that two OWB are competitively superior to three common native prairie species providing them with the ability to invade and threaten the native grasslands of the Central and Southern Great Plains.

/pdf/competitive-abilities-of-native-grasses-and-non-native-3hpk50la82.pdf

Rob Channell

Papers

Dynamic biogeography and conservation of endangered species

Trajectories to extinction: spatial dynamics of the contraction of geographical ranges

Splendid Isolation: Patterns of Geographic Range Collapse in Endangered Mammals

Effects of old world bluestem (bothriochloa ischaemum) on food availability and avian community composition within the mixed-grass prairie

Competitive abilities of native grasses and non-native (Bothriochloa spp.) grasses