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Water is a vital ingredient for thriving plant and animal life. However, in many regions it is in scarce supply. Xerophytes, plants adapted to drought conditions such as the cactus, have a number of adaptations to deal with water scarcity. Cacti may have spines to reduce transpiration and discourage grazing. Succulents have stems and leaves which can retain water and a waxy cuticle to reduce transpiration. Evergreen trees have needle-like leaves also to reduce transpiration during the dry winter season.
c). Evergreen Trees
Temperature influences the rate of physiological processes. Animals that can maintain a fairly consistent temperature may do so by harnessing their metabolism. Mammals are one example of these so-called warm-blooded species. However, cold-blooded species, such as reptiles, must acquire their heat from their environment. Thus reptiles can often be seen "sunning" themselves to raise their temperatures.
Lizard sunning itself on a rock
Interaction Among Species - Competition
Species with their competing needs and drive to perpetuate their species compete on a variety of levels. Individuals of the same species may compete for resources in intra-species competition. However, different species may also compete in order to establish new territory and so acquire new resources.
The purple loosestrife is a plant introduced to the waterways of North America. Originally a garden plant, its vigorous growth and extensive root system out-competes many native plants. In many regions it is seen as a significant problem invader.
Interaction Among Species - Competition
Predation, Parasitism, and Herbivory
Species may also interact by using other animals as a source of energy such as by preying upon them. When a cheetah feeds upon a hyena it is acquiring energy indirectly from the plants the hyena grazed upon. Grazing requires large amounts of time to indirectly acquire the energy of the Sun that the plant attained through photosynthesis.
However, parasitism also sees one organism acquire energy from another, though not by killing the objective organism outright. Mistletoe is a parasitic plant that acquires its resources by growing on trees.
Cheetah chasing hyena
Bogs are waterlogged areas that are characterized by sphagnum mosses and large accumulations of organic matter. Although some bogs remain as wetlands for long periods of time, in many cases the growth of vegetation eventually leads to the establishment of grasses, shrubs and eventually trees. This change over time is referred to as succession.
*See animation on bog succession in the geodiscoveries section of your text’s website.
Evolution, first proposed by Charles Darwin, is based upon the way that a varied population of individuals will react and survive according to conditions and their ability to survive. A modern example is the peppered moth which in unpolluted regions is light grey, but occurs in polluted regions as black. Variation within the species creates both forms, but only the black form survives if forced to live on blackened surfaces resulting from heavy pollution.
The finches of the Galapagos Islands present an example of allopatric speciation - in other words, the different conditions on different islands led to one colonizing species creating a variety of forms.
In contrast, sympatric speciation sees a large population separated into separate species such as the cichlide fish of the African Rift Valley.
Galapagos Island finches
Cichlid fish from Africa
Extinction is where a species disappears entirely due either to natural or human-induced factors. Dinosaurs became extinct along with a variety of other species including trilobites. These seemingly successful species were unable to maintain a population due to changes in the environment or perhaps other variables.
However, today we see evidence of human-induced extinctions, such as the rapid loss of the Dodo in Martinique due to hunting. Today, the Guam kingfisher can no longer live in Guam due to the arrival of snakes. Although maintained in zoos, the Guam kingfisher is unlikely to be returned to its homeland in the near future.
Some plants and animals now cover large areas because of their success in being dispersed. Coconuts remain viable while they float across the ocean surface and consequently they may be found in a range of tropical locations. Animals may also be dispersed effectively. Rats have found humans and their efficient transportation systems an effective way to reach new territory.
Biogeographic regions have also been created by the processes of continental drift. Consequently, many species over millions of years have maintained similar characteristics though reside in distant regions. The large flightless birds such as the cassowary are exemplary of this process.