The pattern of a few abundant species and many rarer species is a defining characteristic of communities worldwide. These abundant species are often referred to as dominant species. Yet, despite their importance, the term dominant species is poorly defined and often used to convey different information by different authors. In order to survive in the desert, organisms must be able to live with very little water or shade.
Rainfall is less than 50 centimeters per year in the desert, and there are few large trees to provide shade canopies. Large mammals are rare in deserts because of their inability to store water and withstand heat. In the North American desert, the kangaroo rat is particularly well-adapted to life in the desert, and so enjoys relatively high population numbers.
Its diet of desert grass seeds provides enough moisture that it can survive without drinking water. They have exceptional hearing and can jump up to nine feet at once, enabling them to escape from predators. The tundra is the coldest and driest ecological community in the world. The average temperature is degrees Fahrenheit and it can drop to degrees. During some months, the sun barely rises.
Or in fattening up animals, which could convert that energy into meat, dairy or draught power. As the centuries passed, animals and plants domesticated in different locations would coalesce into a kind of agricultural package, says Melinda Zeder, an archaeologist who studies the development of pastoral farming at the Smithsonian Institution.
The crops fed animals. The animals worked the land. Their manure fed the crops. And, says Dr Zeder, as a package, they provided a much more reliable and abundant food source. More food meant more people - who could then expand into new territory, and develop new technologies that produced even more food. It was another virtuous circle, but this time powered by the solar energy captured through agriculture.
The surplus energy it created meant we could sustain much larger populations, and what's more, not everyone needed to farm. People could specialise in making tools, building houses, smelting metals or, for that matter, telling other people what to do. Civilisation was developing and with it some fundamental changes in the relationships between people. Hunter gatherer communities tend to share resources fairly equally. In farming communities, by contrast, deep inequalities can develop.
Those who worked long hours in the fields would naturally want to hoard their grain. And then there were those with metal weapons who took a cut from those granaries in the form of taxation. In fact, for thousands of years, the standard of living for the vast majority people on Earth did not improve significantly, despite the bounty of agriculture.
By comparison, a Neolithic, Iron Age, Roman or Saxon farmer would be doing at least double that, she believes. Only kings and nobles lived the kind of affluent, leisurely lifestyles that more and more of us enjoy today. It would take an explosive shift in energy use to achieve that, a shift powered by fossil fuels. By the 18th Century, our increasingly populous societies were beginning to run up against the limits of what the energy provided by the daily influx of the Sun's rays could do.
A Malthusian reckoning loomed. How could we grow food fast enough to feed all those mouths? Or indeed wood to build all our houses and ships, and to make the charcoal to smelt all our metal tools? So we began to turn instead to a black rock that we could dig up and burn in almost unlimited quantities.
Coal contains the solar energy captured over millions of years by fossilised forests. In the 20th Century, the black stuff would be succeeded by those even richer geological stores of photosynthetic energy - oil and natural gas. Toad fish consume mud crabs lethal effect and also cause mud crabs to seek refuge within the reef matrix and stop foraging non-lethal effect. Both of these effects benefit juvenile oysters by reducing predation on them by mud crabs.
In the fields of New England, spiders reduce grasshopper consumption of vegetation by eating grasshoppers, thereby reducing their numbers directly, and by causing the grasshoppers to seek refuge and stop foraging. Indeed the effects of wolves on elk grazing in Yellowstone Park appear to be mediated more by a reluctance of elk to venture into open meadows to forage than by direct predation on elk by wolves.
Finally, flies in the family Phoridae are parasitoids of fire ants and many studies have examined their usefulness as biological control of fire ants. In these examples, it is clear that predators can have significant effects on the composition of entire communities by consuming lower trophic levels, and by altering the behavior or habitat selection of prey.
Understanding how predators affect communities remains a central goal of contemporary ecology as changes in predator population densities or predator behavior may have significant effects on entire ecosystems. Many predator species are in decline globally, and conservation of these important species will likely be essential to insure the long-term stability of freshwater, marine, and terrestrial ecosystems.
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