Our data support the hypothesis of the persistence of L ..
Habitat diversity and species diversity: testing the competition hypothesis with juvenile salmonids
Hypothesis #4: A Reduced supply of ..
It is Vrba’s special insight that ecosystem decay and fragmentation may lead, not only to habitat tracking in and out of a region, and to true extinction, but to true speciation as well. Recall that fragmentation of a species’ original geographic range, as first developed fully by Dobzhansky and Mayr, is a prerequisite to allopatric speciation. Also, note the date of this African disturbance: 2.5 million years ago — just when the Isthmus of Panama rose — and, according to some geologists, created the Gulf Stream, thought by some to have triggered the global cooling pulse that had such a profound effect on the African biota. Elsewhere, I have also suggested that the patterns of speciation in South America that occasioned Hafner’s “refugium” hypothesis in all likelihood reflect the very same sets of ecological and evolutionary processes - through the very same causes12 — as documented and discussed by Vrba.11
This hypothesis was well accepted in 1960’s as studies with electron microscope confirmed that spirochetes were in the connective and epithelial tissues of patients with acute necrotizing ulcerative gingivitis while they are absent in the controls with healthy periodontium.
Ecology/Species Richness and Diversity - Wikibooks, …
For example, the zebra Equus oldowayensis had large and tall teeth specialized for eating grass. Its last known appearance in the fossil record of southern Kenya is between 780,000 and 600,000 years ago; it was replaced by Equus grevyi, which can graze (feed on grass) as well as browse (feed on leaves and other high-growing vegetation). The fossil baboon Theropithecus oswaldi, which weighed over 58 kg (over 127.6 pounds), lived on the ground exclusively; it had very large teeth and consumed grass. It also went extinct between 780,000 and 600,000 years ago. Its extant relative, Papio anubis, is omnivorous and moves easily on the ground and in trees. Two other large-bodied animals that specialized in eating grass, the elephant Elephas recki and the ancient pig Metridiochoerus, were also replaced by related species that were smaller and had more versatile diets (Loxodonta africana and Phacochoerus aethiopicus). The aquatic specialist Hippopotamus gorgops was replaced by the living hippopotamus, which is capable of traversing long distances between water bodies.
An example of a hillside of sediments in the Olorgesailie region. The hillside, which represents about 10,000 years of time with a volcanic ash at its base dated around 1 million years ago, shows evidence of strong environmental shifts. Inset: Layers of sediments show the fluctuation between dry and wet environments and a time when volcanic ash covered the ancient landscape.
06/03/2017 · Ecology/Species Richness and Diversity
The benefits of species diversity can be approached from twoangles, one is the Cost Benefit approach of our monetary basedvalue system, and the other is the Safe Minimum Standard whichholds each species as irreplaceable and worthy of preservationfor its own sake. The cost benefit analysis would be quite adequateif all the costs and benefits were included, but many benefitsare not known and the potential benefits cannot be known. Forexample, in 1970 Grassy Stunt devastated rice crops in India andIndonesia. Severe famine was averted by the development of a resistantstrain. After testing 6,273 varieties, the resistant gene wasfound in only one variety discovered in 1966.
The starting-point for the analysis, she explained, was the forest refugia hypothesis put forward by German scientist JÃ¼rgen Haffer in 1969 and independently by Brazilian scientist Paulo Vanzolini a few months later. According to this theory, climate change in the Pleistocene altered the distribution of tropical forests such as the Amazon and Atlantic Rainforests. These biomes expanded to the utmost during periods of warm wet weather and dwindled to relatively small fragments in cold periods.
From Wikibooks, open books for an open world ..
The Area Hypothesis explains species diversity relative to land area.
Vol 95 Issue 1
Ecological effects of biodiversity - Wikipedia
These ecological effects of biodiversity in turn are affected by both climate ..
Intermediate disturbance hypothesis - Wikipedia
Habitat heterogeneity, species diversity and null …
PPT - Bird Diversity and Habitat PowerPoint …
The spatial heterogeneity hypothesis predicts a positive relationship between habitat complexity and species diversity: the greater the heterogeneity of a habitat, the greater the number of species in that habitat. On a regional scale, this hypothesis has been proposed to explain the increase in species diversity from the poles to the tropics: the tropics are more diverse because they contain more habitats. On the local scale, the spatial heterogeneity hypothesis suggests that the tropics are more diverse because they contain more microhabitats. The positive relationship between habitat heterogeneity and species diversity, on the local scale, is well documented. In this paper, we test whether habitat heterogeneity on the local scale can explain the latitudinal gradient of species diversity on the regional scale. We determined the latitudinal gradient of species diversity of 305 species of North American grasshoppers using published distribution maps. We compared the slope of this multihabitat (regional-scale) gradient with the slope of a withinhabitat (local-scale) gradient in the prairie grasslands. Our results show no significant difference between the slopes at the two scales. We tested the generality of our results by comparing multi- and within-habitat latitudinal gradients of species diversity for ants, scorpions and mammals using data from the literature. These results are in accordance with those from grasshoppers. We can therefore reject the local-scale spatial heterogeneity hypothesis as a mechanism explaining the regional-scale latitudinal gradient of species diversity. We discuss alternative mechanisms that produce this gradient.
18/10/1998 · Bird diversity and environmental ..
Species extinctions are very difficult to quantify. In the past the man caused extinctions have been primarily due to hunting. As man crossed over from Asia and entered the North American Continent, a series of extinctions occurred caused in part by man's predation of slow moving species like the mammoth and other mega-herbivores and perhaps, according to a new hypothesis, by the introduction of new diseases by man or his domesticated animals. The loss of these species caused other dependent species to go extinct like the giant vultures and the long nosed bear. A similar wave of extinctions happened as the Polynesians colonized the pacific islands. This time it was the flightless birds that were defenseless against the new predators. The Moa was the largest, but on many islands there is evidence that up to 50% of all species of birds were hunted to extinction including such remarkable species as the Hawaiian Eagle.
namely the species diversity–energy hypothesis, ..
By Karina Toledo Â | Â AgÃªncia FAPESP – Evidence in the scientific literature supports the hypothesis that the Pleistocene, the geological epoch which lasted from about 2.5m to 11,700 years ago, spanning the most recent global glaciations, was a time of radical climate change, when very cold and dry periods alternated with very warm and wet periods.
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