Timothy M. Crowe
Bio: Timothy M. Crowe is an academic researcher from University of Cape Town. The author has contributed to research in topics: Francolin & Helmeted guineafowl. The author has an hindex of 27, co-authored 93 publications receiving 2628 citations. Previous affiliations of Timothy M. Crowe include American Museum of Natural History & DST Systems.
Papers published on a yearly basis
TL;DR: The combined‐data cladogram supports the hypothesis that basal lineages of galliforms diverged prior to the Cretaceous/Tertiary (K‐T) Event and that the subsequent cladogenesis was influenced by the break‐up of Gondwana.
Abstract: The phylogenetic relationships, biogeography and classification of, and morpho- behavioral (M/B) evolution in, gamebirds (Aves: Galliformes) are investigated. In-group taxa (rooted on representatives of the Anseriformes) include 158 species representing all suprageneric galliform taxa and 65 genera. The characters include 102 M/B attributes and 4452 nucleic acid base pairs from mitochondrial cytochrome b (CYT B), NADH
TL;DR: The molecular phylogenetic analyses indicated that the pheasants and partridges arose through a rapid radiation, making it difficult to establish higher level relationships, but was able to establish six major lineages containing pheasant and partridge taxa.
Abstract: Cytochrome b and D-loop nucleotide sequences were used to study patterns of molecular evolution and phylogenetic relationships between the pheasants and the partridges, which are thought to form two closely related monophyletic galliform lineages. Our analyses used 34 complete cytochrome b and 22 partial D-loop sequences from the hypervariable domain I of the D-loop, representing 20 pheasant species (15 genera) and 12 partridge species (5 genera). We performed parsimony, maximum likelihood, and distance analyses to resolve these phylogenetic relationships. In this data set, transversion analyses gave results similar to those of global analyses. All of our molecular phylogenetic analyses indicated that the pheasants and partridges arose through a rapid radiation, making it difficult to establish higher level relationships. However, we were able to establish six major lineages containing pheasant and partridge taxa, including one lineage containing both pheasants and partridges (Gallus, Bambusicola and Francolinus). This result, supported by maximum likelihood tests, indicated that the pheasants and partridges do not form independent monophyletic lineages.
TL;DR: The results suggest that aridification of Africa in response to glaciation at higher latitudes during the Pleistocene has had a profound influence on montane speciation in east and central Africa.
Abstract: Although many studies have documented the effect of glaciation on the evolutionary history of Northern Hemisphere flora and fauna, this study is the first to investigate how the indirect aridification of Africa caused by global cooling in response to glacial cycles at higher latitudes has influenced the evolutionary history of an African montane bird. Mitochondrial DNA sequences from the NADH 3 gene were collected from 283 individual Starred Robins (Pogonocichla stellata, Muscicapoidea). At least two major vicariant events, one that separated the Albertine Rift from all but the Kenyan Highlands around 1.3–1.2 Myrs BP, and another that separated the Kenyan Highlands from the northern Eastern Arc, and the northern Eastern Arc from the south-central Eastern Arc between 0.9 and 0.8 Myrs BP appear to underlie much of the observed genetic diversity and structure within Starred Robin populations. These dates of divergence suggest a lack of recurrent gene flow; although the Albertine Rift and south-central Eastern Arc share haplotypes, based on coalescent analyses this can confidently be accounted for by ancestral polymorphism as opposed to recurrent gene flow. Taken collectively, strong evidence exists for recognition of four major ancestral populations: (1) Kenyan Highlands (subspecies keniensis), (2) Albertine Rift (ruwenzori), (3) northern Eastern Arc (helleri), and (4) south-central Eastern Arc, Ufipa and the Malawi Rift (orientalis). The estimated divergence times cluster remarkably around one of the three estimated peaks of aridification in Africa during the Plio-Pleistocene centred on 1 Myrs BP. Further, time to most recent common ancestor (TMRCA) estimates (1.7–1.6 Myrs BP) of gene divergence between the Albertine Rift and the other montane highlands corresponds closely with a second estimated peak of aridification at about 1.7 Myrs BP. Collectively, these results suggest that aridification of Africa in response to glaciation at higher latitudes during the Pleistocene has had a profound influence on montane speciation in east and central Africa.
TL;DR: An emerging phylogenetic picture reveals that relationships within Old World families are highly informative regarding the early dispersal and radiation of songbirds out of Gondwana.
Abstract: The deep divergence between the African endemic passerines Picathartidae (rockfowl Picathartes and rockjumpers Chaetops, four species) and the Passerida (ca. 3500 species) suggests an older history of oscines on the African continent than has previously been assumed. In order to determine whether any additional, unexpectedly deep lineages occur in African endemic songbirds, 29 species—including 10 enigmatic focal taxa endemic to southern Africa—were added to a large nuclear sequence dataset gathered from oscine songbirds (Passeri). Phylogenetic analyses of these data resolve many long-standing questions about the affinities of these birds, not all of which were predicted by traditional approaches. The application of a molecular clock indicates that most basal divergences in Passerida occurred in the middle to late Eocene, with divergences between African and Australasian core corvoids occurring somewhat later in the early Miocene. Consistent with inferences for mammals, divergences between Malagasy endemic passerines and their mainland relatives suggests an asynchronous colonization history. This emerging phylogenetic picture reveals that relationships within Old World families are highly informative regarding the early dispersal and radiation of songbirds out of Gondwana. Future analyses will depend on improving resolution of higher-level phylogenetic relationships among these groups, and increasing the density of taxon sampling within them.
TL;DR: A ‘silver bullet’ strategy on the part of conservation planners, focusing on ‘biodiversity hotspots’ where exceptional concentrations of endemic species are undergoing exceptional loss of habitat, is proposed.
Abstract: Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.
TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
Abstract: 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
TL;DR: It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
Abstract: The relationship between the two estimates of genetic variation at the DNA level, namely the number of segregating sites and the average number of nucleotide differences estimated from pairwise comparison, is investigated. It is found that the correlation between these two estimates is large when the sample size is small, and decreases slowly as the sample size increases. Using the relationship obtained, a statistical method for testing the neutral mutation hypothesis is developed. This method needs only the data of DNA polymorphism, namely the genetic variation within population at the DNA level. A simple method of computer simulation, that was used in order to obtain the distribution of a new statistic developed, is also presented. Applying this statistical method to the five regions of DNA sequences in Drosophila melanogaster, it is found that large insertion/deletion (greater than 100 bp) is deleterious. It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
TL;DR: A review by Czech and colleagues (2000) finds that urbanization endangers more species and is more geographically ubiquitous in the mainland United States than any other human activity, emphasizing the uniquely far-reaching transformations that accompany urban sprawl as discussed by the authors.
Abstract: A the many human activities that cause habitat loss (Czech et al. 2000), urban development produces some of the greatest local extinction rates and frequently eliminates the large majority of native species (Vale and Vale 1976, Luniak 1994, Kowarik 1995, Marzluff 2001). Also, urbanization is often more lasting than other types of habitat loss. Throughout much of New England, for example, ecological succession is restoring forest habitat lost from farming and logging, whereas most urbanized areas in that region not only persist but continue to expand and threaten other local ecosystems (Stein et al. 2000). Another great conservation challenge of urban growth is that it replaces the native species that are lost with widespread “weedy” nonnative species. This replacement constitutes the process of biotic homogenization that threatens to reduce the biological uniqueness of local ecosystems (Blair 2001). Urban-gradient studies show that, for many taxa, for example, plants (Kowarik 1995) and birds and butterflies (Blair and Launer 1997), the number of nonnative species increases toward centers of urbanization, while the number of native species decreases. The final conservation challenge of sprawl is its current and growing geographical extent (Benfield et al. 1999). A review by Czech and colleagues (2000) finds that urbanization endangers more species and is more geographically ubiquitous in the mainland United States than any other human activity. Species threatened by urbanization also tend to be threatened by agriculture, recreation, roads, and many other human impacts, emphasizing the uniquely far-reaching transformations that accompany urban sprawl. About 50% of the US population lives in the suburbs, with another 30% living in cities (USCB 2001). Over 5% of the total surface area of the United States is covered by urban and other built-up areas (USCB 2001). This is more land than is covered by the combined total of national and state parks and areas preserved by the Nature Conservancy. More ominously, the growth rate of urban land use is accelerating faster than land preserved as parks or conservation areas by the Conservancy (figure 1). Much of this growth is from the spread of suburban housing. It is estimated, for example, that residential yards occupy 135,000 acres in the state of Missouri (MDC 2002). This residential landscape represents nearly 1% of the total area of Missouri and is nearly three times the area occupied by Missouri state parks. Here I review the growing literature that documents how urban (and suburban) expansion harms native ecosystems. This knowledge can aid conservation efforts in two major ways. One is through the use of ecological principles—such as preserving remnant natural habitat and restoring modified habitats to promote native species conservation—to reduce the impacts of urbanization on native ecosystems. Rare and endangered species sometimes occur in urbanized habitats (Kendle and Forbes 1997, Godefroid 2001) and thus could be conserved there. Managing the large amount of residential vegetation (1% of the state area, as noted above) in ways that promote native plants and animals could also make a significant contribution to conservation.
TL;DR: In this paper, a basic conservation challenge is that urban biota is often quite diverse and very abundant, and that, because so many urban species are immigrants adapting to city habitats, urbanites of all income levels become increasingly disconnected from local indigenous species and their natural ecosystems.
Abstract: When measured by extent and intensity, urbanization is one of the most homogenizing of all major human activities. Cities homogenize the physical environment because they are built to meet the relatively narrow needs of just one species, our own. Also, cities are maintained for centuries in a disequilibrium state from the local natural environment by the importation of vast resources of energy and materials. Consequently, as cities expand across the planet, biological homogenization increases because the same “urban-adaptable” species become increasingly widespread and locally abundant in cities across the planet. As urbanization often produces a local gradient of disturbance, one can also observe a gradient of homogenization. Synanthropic species adapted to intensely modified built habitats at the urban core are “global homogenizers”, found in cities worldwide. However, many suburban and urban fringe habitats are occupied by native species that become regionally widespread. These suburban adapters typically consist of early successional plants and “edge” animal species such as mesopredator mammals, and ground-foraging, omnivorous and frugivorous birds that can utilize gardens, forest fragments and many other habitats available in the suburbs. A basic conservation challenge is that urban biota is often quite diverse and very abundant. The intentional and unintentional importation of species adapted to urban habitats, combined with many food resources imported for human use, often produces local species diversity and abundance that is often equal to or greater than the surrounding landscape. With the important exception of low-income areas, urban human populations often inhabit richly cultivated suburban habitats with a relatively high local floral and faunal diversity and/or abundance without awareness of the global impoverishment caused by urbanization. Equally challenging is that, because so many urban species are immigrants adapting to city habitats, urbanites of all income levels become increasingly disconnected from local indigenous species and their natural ecosystems. Urban conservation should therefore focus on promoting preservation and restoration of local indigenous species.