Chapter 5 Evolution of Biodiversity

Biodiversity is a key indicator of environmental health Biodiversity is critical to our survival. We depend on it for almost everything: food, fuel, clothing, building materials and medicines to name but a few. Biodiversity is also very important to our quality of life. The number of species in any given place is the most common measure of biodiversity. The insect group contains more species than most other groups

The total number of Insects species is estimated to be over 30 million!

Species Richness vs Species Eveness Species RichnessSpecies Evenness The number of species in a given area The relative proportions of individuals within the different species Indicates the approximate sense of the biodiversity of a particular place Indicates whether a particular ecosystem is dominated by one species or whether all species have similar abundance Can help scientists evaluate impact of a disturbance Both species richness and evenness can be measured using the Shannon- Weiner Index of Biodiversity.

Phylogenetic tree Phylogenetic trees show how different groups of organisms are related and show where speciation occurred.

Evolution is the mechanism underlying biodiversity Microevolution- evolution below the species level (varieties of different apples or potatoes) Macroevolution- genetic changes gives rise to new species(speciation), genera, families, classes or phyla Genetic diversity is created by mutation(random change in the genetic code which can be caused by UV radiation from the sun) and recombination(when part of a chromosome breaks off and attaches to another chromosome during replication and can produce novel traits.

Artificial SelectionNatural SelectionRandom Processes Humans determine which individual breed with a preconceived set of traits in mind Ex: Labradoodle The environment determines which individuals survive and reproduce Ex: Survival of the Fittest The genetic composition of a population still changes over time, but the changes are not related to differences in the fitness among individuals. Most of our agricultural crops are the result of careful breeding Theory developed by Darwin in 1859-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, differences in traits are associated with differences in the ability to survive and reproduce. Examples: Mutation, Genetic Drift( change in the genetic composition of a population over time as a result of random mating), Bottleneck effect(a reduction in genetic diversity of a population caused by a reduction in population size), Founder effect (a change in population descended from a small amount of colonizing individuals) Has led to unwanted results: resistant strains And other unintended results Natural selection favors any combination of traits that improves an individual fitness= adaptation Evolution by different processes

Speciation and extinction determine Biodiversity Allopatric vs Sympatric Speciation Allopatric Speciation: when geographic isolation(separating a population by a geographic barrier change)creates new species. When this occurs eventually the populations from the older area and the newer area can no longer breed and are in reproductive isolation. The 2 populations become 2 distinct species. This is the most common way evolution generates new species.* Sympatric Speciation: the evolution of one species into two species in the absence of geographic isolation, usually through a process called polyploidy (the number of chromosomes increases to multiple sets instead of the usual diploid number, accidently or with human intervention). Once polyploid, these organisms can no longer breed with diploid ancestors and become reproductively isolated.**

Allopatric Populations Allopatric speciation is just a fancy name for speciation by geographic isolation. In this mode of speciation, something extrinsic to the organisms prevents two or more groups from mating with each other regularly, eventually causing that lineage to speciate. Isolation might occur because of great distance or a physical barrier, such as a desert or river.

In Sympatric Speciation the separation is non- geographical but more "behavioral" or "social". This form of speciation is believed to be particularly significant in the evolution of insect species. Ex: Many herbivorous insects lay their eggs on a particular plant variety so that when the larvae hatch they have a readily available food supply. Mating may also take place on the same plants. The larvae become imprinted with this plant and when they reach adulthood they in turn will lay their eggs on the same plant. Sympatric Populations

If an adult makes a mistake and lays its eggs on the wrong plant, all subsequent generations will become imprinted with the same wrong plant. This behavioral-related separation results in the insects on the "wrong" plants being separated from the original group so that over time speciation occur.

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The Pace of Evolution A significant change in a species genotype and phenotype can take anywhere from hundreds to millions of years. Average global rate of evolution is about one new specie every 3 million years. The ability of a specie to survive an environmental change depends greatly on how quickly it evolves the adaptations needed to thrive and reproduce under the new conditions.

To survive a rapid environmental change, a population must evolve adaptations quickly or go extinct. Successful adaptation depends on 4 factors: Rate of environmental change: if it happens too quickly, most species do not have time to adapt and will go extinct Genetic Variation: High levels of genetic variation ensures that some individuals will be well suited to the new environment and allows for more rapid evolution by natural selection. Population size: if a small population experiences a mutation, it can spread more quickly because the individual with the mutation will breed with a number of mates that represent a large proportion of the entire population. Generation time: If the time between generations is small, the change in genetic composition of a species, occurs more quickly.

Genetic Engineering Evolution occurs even more rapidly in populations of genetically modified organisms. Scientists can insert genes with desirable traits into organisms w/o them to produce genetically modified organisms. These organisms will pass on the new traits to their offspring. Obviously this is much quicker than traditional plant breeding which can only select from the naturally available variations in a population.

Evolution shapes ecological niches and determines species distributions The fundamental niche of a species is the ideal range of abiotic conditions such as temperature, humidity, salinity, and pH under which members can survive, grow and reproduce). As conditions move away from the ideal, individual may be able to survive but not grow or reproduce. The addition of biotic factors more narrowly defines the parts of the fundamental niche that a species actually use. The range of abiotic and biotic conditions which a species actually lives is a realized niche.

Fundamental and Realized Niche

Some species live under a very wide range of abiotic and biotic conditions(niche generalists) while others can live under a very narrow range (niche specialists). Niche specialists are vulnerable to extinction if conditions change. Changes in environmental conditions have led to distribution changes in species in the past. We can predict with an increase in global temperatures, this pattern will continue. Some species can move physically more quickly than others to adapt to these climatic changes and shift their distribution pattern

Distribution model of the yellow throated vireo This specie can live under a wide variety of conditions.

Environmental changes and Species Extinctions If environmental conditions change and species cannot move or adapt, they go extinct. 99% of species that have ever lived on earth are now extinct. Throughout Earth’s history, the fossil record indicates there have been 5 periods of global mass extinction. The greatest mass extinction occurred 251 million years ago. 90% of marine and 70% of land vertebrates went extinct. 65 million years ago (end of the Cretaceous period) the dinosaurs went extinct along with 50% of earth’s species. Scientists think we are experiencing another mass extinction now and during the last 2 decades as a result of habitat destruction, over harvesting, climate changes and emerging diseases.

Fossils Data shows 5 Prior mass extinctions

Diversity of Marine Animals and Extinction

Sea level drops and mass extinction