Chapter 7 Biological Diversity

Biological Diversity Biological Diversity The variety of life-forms commonly expressed as the number of species in an area (the genes they contain and the ecosystems they live in)

Biological Evolution Biological Evolution (Charles Darwin) The change in inherited characteristics of a population from generation to generation Can result in new species

Four Processes that Lead to Biological Evolution Mutation Natural Selection Migration Genetic Shift

Mutation A chemical change in a DNA molecule Affects the expressed characteristics (genotype) when cells or individual organisms reproduce

Natural Selection Genetic Variability May allow an organism to adapt Organisms whose biological characteristics make them better able to survive and reproduce (leave more offspring) 4 Characteristics that allow/cause NS to occur: Genetic Variability May allow an organism to adapt Environmental Variability changes to the environment (seasons) Differential Reproduction those organisms best adapted to the environment will have a better chance to reach reproductive age Environmental Influence changes to environment over time Species: a group of individuals that reproduce with each other

Migration Two population of the same species become geographically isolated from each other for a long period of time. New species evolve from an original species due to this isolation Ex: land bridge b/w Alaska and Siberia, when the bridge was cut off – new species formed

Genetic Drift Changes in the frequency of a gene in a population due to chance Ex: isolation of bighorn sheep in mountains due to human activities. Isolation is in small groups and therefore a small gene pool. Reduces genetic variability and therefore the ability to adapt to future changes. AND less adaptive characteristics may dominate Can be a problem for rare or endangered species

Genetic Drift Example

Basic Concepts of Biological Diversity Genetic Diversity total # of genetic characteristics of a specific species. (Total # of genes) Habitat Diversity The different kinds of habitats in a given area Species Diversity – Three Qualities : Species Richness – total # of species Species Evenness – relative abundance of a species Species Dominance- the most abundant species

The Number of Species on Earth No one knows the exact number About 1.4 million – 1.8 million species have been identified and named Insects and plants make up most of these species Number will increase

Why are there so many species?? If species compete for resources, wouldn’t the losers die off ?????? The answer lies in the way they interact Competition, predation, parasitism, mutualism and commensalism

Ecological Niche and Habitat Habitat: where a species lives Ecological Niche: The sum of all a species tolerance ranges, under which they can survive in an ecosystem. The reason more species do not die out from competition is that they have developed a niche, and thus avoid competition

Species Engage in 3 Basic Interactions 1. Competition 2. Symbiosis – mutualism & commenselism 3. Predation-Parasitism Each affect evolution, persistence of a species and the overall diversity of life Organisms have evolved together and therefore adjusted to one another Human interventions upset these adjustments

Competition Organisms vie for the same limited resources in an environment – food, nutrients, space, sunlight

The Competitive Exclusion Principles 2 species that have exactly the same requirements cannot coexist in exactly the same habitat Ex) introduction of the gray squirrel into Great Britain

Symbiosis The relationship between 2 organisms that is beneficial to both and enhances each organisms chances of persisting Obligate symbionts: a symbiotic relationship between two organisms in which neither by themselves can exist without the other Ex) stomach of a reindeer

Types of Symbiosis Mutualism – Two organisms interact in a manner that is beneficial to both Birds removing ticks from the back of a Rhino Bacteria or protozoa living in the gut of an animal Commenselism – Two organisms interact and it benefits one, but has no impact on the other Plants that live on the roots of other plants to obtain more water

commensalism

Parasitism One organism gains energy by living on or inside a host organism. Ticks on mammals Hookworms inside mammals Parasites are much smaller than their hosts and rarely kill them

Predation An organism feeds on part or all of another organism (prey) Unique strategies for survival Pursuit and ambush Mimicry Camouflage Chemical Warfare (poisons)

Environmental Factors that affect biodiversity Increase biodiversity: Physically diverse habitat Moderate amts. Of disturbance Sm. Variation in environmental conditions High diversity in one trophic level (increase diversity in other levels) Environment highly modified by life Middle stages of succession evolution

Environmental Factors that affect biodiversity Decreases biodiversity: Environmental stress Extreme environments Severe limitations in a supply of an essential resource Extreme amounts of disturbance Recent introduction of exotic species Geographic isolation

Interrelationships among climate, geology, soil, vegetation and animals

Ecological gradient: change in the relative abundance of a species over an area or a distance