Lecture -7: Biological Diversity and Biogeography ENV 107: Introduction to Environmental Science Dr. A.K.M. Saiful Islam
Biological Evolution Refers to the change in inherited characteristics of a population from generation to generation. Along with self-reproduction, biological evolution is one of the features that distinguish life from everything else in the universe. Biological evolution is a one-way process. One species extinct, it is gone forever.
7.2 Process that lead to Evolution: 1. Mutation Genes contained chromosomes within cells, are inherited from one generation to the next. Genes are made up of complex chemical compound called deoxyribonucleic acid (DNA), which made up of chemical building blocks that form a code, or kind of alphabetic information. External agents such as radiation or certain toxic organic chemicals, comes in contact with DNA and alters it. When DNA changes, it is said to have undergone mutation. It can result in a new species whether or not that species is better adapted than its parental species to the environment.
2. Natural Selection Natural selection is a process by which organisms whose biological characteristics better fit them to the environment are better represented by descendants in future generations than are those whose characteristics are less fit for the environment. Figure 72. Dark variation of birds are dominant in polluted urban areas and light natural coloration of bird in rural region illustrates the features of biological evaluation (natural selection) due industrial mechanism.
ENV 107:Introduction to Environmental Science Dr. Akm Saiful Islam Industrial Melanism and Natural Selection
3. Migration The migration of one population of a species into a habitant previously occupied by another population is a process that lead to change in gene frequency. Even organisms that do not move themselves may have reproductive structures that migrate. For example, seeds of flowering plants for example are blown by the wind and moved by animals.
4. Genetic Drift Refers to changes in the frequency of a gene in a population as a result of chance rather than mutation, selection or migration. Chance may determine which individuals become isolated in a small group from a larger population and thus which genetic characteristics are most common in that isolated population. The individuals may be better, poorly or neutrally adapted to the environment. For example bighorn sheep live in the mountains of the desert southwest of US. Before human settlement, they can migrate and move freely. With human settlement on that region, many population of bighorn sheep have become isolated and that cause problem to their survival.
Biological Diversity Biological Diversity involves three concepts: Genetic diversity: the total number of genetic characteristics, sometimes of a specific species, subspecies, or group of species. Habitat diversity: the diversity of habitats in a given unit area. Species diversity: which has three aspects: Species richness the total number of species Species evenness the relative abundance of species Species dominance the most abundant species
Terms related to Species Habitat Exotic species: - a species introduced into new geographic area. Endemic Species: - a species that is native to a particular area and not native elsewhere is called an endemic species. For example, Monterey pine is endemic to a portion of the California coast and exotic in New Zealand. Cosmopolitan species: - a species with a broad distribution, occurring all over the world wherever the environment is appropriate. For example, the moose is found in both North America and Europe and is therefore a cosmopolitan. Ubiquitous Species: - species that are found almost anywhere. For example, human are ubiquitous as are some bacteria.
Interactions between species There are three basic kinds of interactions between species Competition in which the outcome is negative for both groups. Symbiosis which benefits both participants Predation-parasitism in which the outcome benefits one and is detrimental to the others.
Competitive exclusion: Squirrel (a) American gray squirrel (b) European red squirrel
Competitive exclusion of flour beetle A: Likes warm, dry condition B: Likes cool, wet condition Both: Like to eat wheat In uniform environment, one will Win out over other In a mixed environment, the Beetles will use separate parts Of the habitat In either case, beetles do not coexists
Results under warm dry condition
Reindeer and Symbiotic Bacteria
Environmenatal factors that influence diversity A. Factors that tend to increase diversity 1. A physically diverse habitant 2. Moderate amounts of disturbance (such as fire or storm) 3. A small variation in environmental condition (temperature, precipitation etc) 4. High diversity at one trophic level increase the diversity at another trophic level 5. An environmental highly modified by life (for example a rich organic soil). 6. Middle stages of succession. 7. Evolution.
Environmenatal factors (cont..) B. Factors that tend to decrease diversity 1. Environmental stress. 2. Extreme environments (conditions near to limit of what living things can withstand). 3. A severe limitations in the supply of an essential resources. 4. Extreme amount of disturbance. 5. Recent introduction of exotic species (species from other area). 6. Geographic isolation.