# Evolution of Biodiversity

## Presentation on theme: "Evolution of Biodiversity"— Presentation transcript:

Evolution of Biodiversity
Chapter 5

What is biodiversity? Biodiversity refers to the variety of organisms on Earth Three different scales: Ecosystem diversity- the variety of ecosystems within a given region. Species diversity- the variety of species in a given ecosystem. Genetic diversity- the variety of genes within a given species.

How much biodiversity? Earth is home to a tremendous diversity of species; current estimates range between million species 1.5 million identified and named so far: Insects are most diverse group

C. Measuring local or regional species biodiversity
Species richness - total number of species in a given area Species evenness - the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals Both decline after human disturbance Knowing values gives environmental scientists baseline to determine change in ecosystems

Methods for Estimating Biodiversity
Simpson Index Shannon-Weiner Index Sampling When estimating population size it is important to collect RANDOM SAMPLES. A sample is a part of a population or part of an area, chosen to illustrate what the whole population or area is like. In a random sample every individual in a population has an equal chance of being selected Using quadrats: Mark out area to be sampled. Place quadrats ( 1 m2, 10 m2) randomly within the area. Count how many individuals are inside each of the quadrats. Calculate the mean number of individuals per quadrat. Pop. Size = mean X total area area of each quadrat

Quadrat sampling is suitable for plants that do not move around and are easy to find.

Knowing population size is important in making environmental decisions that would affect the population. Making a decision on an estimate that is too high = extinction. Making a decision on an estimate that is too low = unnecessarily hurt people that depend on the animals for food & income. Change in the relative abundance of a species over an area or a distance is referred to as an ecological gradient (aka zonation)

How Geology and Geography Affect Biologic Diversity
Species are not uniformly distributed over the earth’s surface; diversity varies greatly from place to place Species and ecosystems on land change with soil type and topography: Slope, aspect (the direction the slope faces), elevation, and nearness to a drainage basin These factors influence the number and type of plants, which in turn influences the number and types of animals

Biological Evolution Refers to the change in inherited characteristics of a population from generation to generation It is the mechanism underlying biodiversity Microevolution- evolution below the species level (e.g. different varieties of apples or potatoes) Macroevolution- evolution which gives rise to new species or new genera, family, class or phyla New species arise as a result of competition for resources and the differences among individuals in their adaptations to environmental conditions

Creating Genetic Diversity (two processes)
Mutation DNA is copied millions of times in an organism’s lifetime as cells divide Random copying “mistakes” are made = change in genes “Good” mutations increase the organism’s chance of survival and reproduction, so the mutation is passed on to next generation Increases population’s genetic diversity Recombination Occurs in plant and animal cells during Prophase I (crossing over) Creates new genetic combinations of genes

Evolution by Artificial Selection (two types)
Artificial selection is when humans select which individuals breed to create desired phenotypes What is genotype and phenotype?

Darwin’s Theory of Natural Selection
Individuals produce an excess of offspring. Not all offspring can survive. Individuals differ in their traits. Differences in traits can be passed on from parents to offspring, and are associated with differences in the ability to survive and reproduce. Natural selection DOES NOT select for specific traits; rather it favors any combo of traits that increases a species fitness Traits that improve fitness = adaptations

Natural Selection

Genetic Drift Change in the genetic composition of a population over time as a result of random mating

Bottleneck effect Reduction in the genetic diversity of a population caused by a reduction in its size.

Founder effect Change in a population descended from a small number of colonizing individuals

Random Evolutionary Processes

Speciation Creation of new species Two types: Allopatric speciation or when new species are created by geographic reproductive isolation.

Sympatric speciation- the evolution of one species into two species in the absence of geographic isolation, usually through the process of polyploidy (an increase in the number of sets of chromosomes)

Pace and Patterns of Evolution
Four factors that influence successful adaptation: Rate of environmental change Genetic variation Population size Generation time Average global rate of evolution is about one new species every 3 million years

B. Evolution shapes ecological niches and determines species distributions
All species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance Fundamental niche - the ideal conditions for a species.

Niche generalist - species that live under a wide range of conditions
Range of abiotic and biotic conditions under which a species lives is its realized niche Determines the species distribution, or areas of the world where it lives Niche generalist - species that live under a wide range of conditions Niche specialist - species that live only in specific habitats. Some species like insects can live in a very wide range of specialized niches, whereas others can only live in a very narrow range Meadow spittlebug 2. Skeletonizing leaf beetle

C. Environmental Change and Species Distribution
Changes in environmental conditions has an effect on species distribution …How do we know? Analyze layers of sediment and find different types of pollen at different strata

As climate change accelerates, precipitation patterns change, but species niche requirements don’t
Predict species distribution

D. Environmental Change and Species Extinction
Average life span of a species is 1-10 million years About 99% of all species that ever lived on Earth are exticnt Much of what we know about evolution comes from the fossil record.

4. The Five Global Mass Extinctions
Mass extinction - when large numbers of species went extinct over a relatively short period of time.

5. The Sixth Mass Extinction
Scientists think we are in our sixth mass extinction, occurring in the last two decades Estimates of extinction rates vary widely, from 2 % to 25% by 2020 In contrast to previous mass extinctions, scientists agree that this one is caused by humans.