Ecosystems – Species Diversity & Environmental Interactions

After this unit you should be able to:

• Explain the process of natural selection and cite evidence for this process

• Describe the ways in which evolution influences biodiversity • Discuss reasons for species extinction and mass extinction events • List the levels of ecological organization • Outline the characteristics of populations that help predict population

growth • Assess logistic growth, carrying capacity, limiting factors, and other

fundamental concepts in population ecology • Identify efforts and challenges involved in the conservation of

biodiversity

Learning Targets:• Natural selection• How evolution influences

biodiversity• Reasons for species

extinction• Ecological organization• Population characteristics• Population ecology• Conserving biodiversity

Organisms and Species• Organisms, the different forms of life on earth,

can be classified into different species based on certain characteristics.

Figure 3-3

Evolution generates biodiversity

• Species = a population or group of populations – Whose members share characteristics – They can breed with one another and produce

fertile offspring• Population = a group of individuals of a species

that live in the same area• Evolution = means change over time

– Biological evolution: genetic change in populations over time

– Genetic changes lead to changes in appearance, functioning or behavior over generations

Natural selection

• Evolution may be seen as random – directed by natural selection

• Natural Selection = traits that enhance survival and reproduction – Are passed on more frequently to future generations – those that do not lead to survival, disappear in the

gene pool.

Evolution by natural selectionMicro-evolution: The concept of change over time.

change is through populations of species, not individuals. Occurs over many generations, through environmental influence and

genetic variation. Micro-evolution can lead to Macro-Evolution (geologically speaking).

• It is one of the best-supported and most informative concepts in all science

– It is the main standpoint of modern biology and the basis for Biodiversity.

– Both, Darwin and Wallace proposed natural selection as the mechanism of evolution

– Knowing ecology and learning the history of life helps us to understand and appreciate environmental science

• Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.

Natural selection shapes organisms• Premises of natural selection:- Organisms struggle to survive and reproduce- Organisms produce more offspring than can

survive- Individuals of a species vary in their

characteristics due to genes and the environment - Some individuals are better suited to their

environment and reproduce more effectively• Natural selection acts on genetic variation

Genetic variation• Adaptation = the process where, over time,

characteristics (traits) that lead to better reproductive success– Become more prevalent in the population

• Adaptive trait (leads to adaptation) = a trait that promotes reproductive success

• Mutations = accidental changes in DNA that may be passed on to the next generation– Non-lethal mutations provide the genetic variation on which

natural selection acts• Sexual reproduction = also leads to variation through

mating preferences.

Natural selection acts on genetic variation• Natural selection changes

characteristics through:• Directional selection =

drives a feature in one direction

• Stabilizing selection = favors intermediate traits– Preserving the status quo

• Disruptive selection = traits diverge in two or more directions

Environmental conditions affect selection

• Environmental conditions determine the pressures natural selection exerts– These pressures affect who survives and reproduces– Traits evolve that allow success in that environment

• But traits that promote success at one time or place may not do so at another

• Natural selection weeds out unfit individuals– It also elaborates and diversifies traits that may produce

new species

Selective pressures influence adaptation

• Divergent evolution = Related species in different environments – Experience different pressures– Evolve different traits

• Convergent evolution = unrelated species may evolve similar traits – Because they live in similar

environments

Evidence of natural selection is everywhere• It is evident in every adaptation of every organism• Artificial Selection = the process of selection

conducted under human direction– Producing the great variety of dog breeds and food

crops

Evolution generates biological diversity

• Biological diversity (biodiversity) = the variety of life across all levels of biological organization– Species– Genes– Environmental

• Scientists have described 1.8 million species– Up to 100 million species may exist– Tropical rainforests are rich in biodiversity

SpeciationSpeciation produces new types of organisms • The process of generating new species

from a single species Geographic Isolation

Where changes and isolations within the environment and habitat cause new species to form.

• Allopatric speciation: species formation due to physical separation of populations– The main mode of speciation– Populations can be separated by glaciers,

rivers, mountains– Each population gets its own set of

mutations

Another type of speciation

• Sympatric speciation = species form from populations that become reproductively isolated within the same area– Feed in different areas or eat different foods.– Mate in different seasons or because of mating rituals.– Hybridization between two species– Mutations

Bird dances: rifle bird ; moonwalk.

Speciation results in diverse life forms• How do major groups diverge over time?• Phylogenetic trees (cladograms) = show

relationships among species, groups, genes, etc.– Scientists can trace how certain traits evolved

The fossil record

• Fossil: an imprint in stone of a dead organism• Fossil record: the cumulative body of fossils

worldwide• The fossil record shows:

– Life has existed on Earth for at least 3.5 billion years– Earlier types of organisms evolved into later ones– The number of species has increased over time– Most species have gone extinct– There have been several mass extinctions in the past

Extinction• Extinction = the

disappearance of a species from Earth– Species last 1-10 million years

• Biological diversity is now being lost at an astounding rate– This loss of species is

irreversible

Number of species = speciation - extinction

Extinction is a natural process, but …

• Humans profoundly affect rates of extinction• Biodiversity loss affects people directly

– Food, fiber, medicine, ecosystem services

Some species are more vulnerable to extinction

• Extinction occurs when the environment changes rapidly– Natural selection can not keep up

• Many factors cause extinction:– Severe weather, climate change, changing sea levels– New species, small populations– Specialized species

• Endemic species = a species only exists in a certain, specialized area– Very susceptible to extinction– These species usually have small populations

Many U.S. amphibian species are vulnerable• Many U.S. amphibians have very small ranges

– They are vulnerable to extinction– The Yosemite toad, Houston toad, Florida bog frog

• 40 salamander species are restricted to areas the size of a typical county

Some U.S. salamander species live on top of single mountains

Striking gold in Costa Rica• In 1964, Golden toads

were discovered in Monteverde, Costa Rica

• The mountainous cloud forest has a perfect climate for amphibians

• They became extinct within 25 years – Climate change’s drying

effect on the forest– A lethal fungus