Ecosystems species diversity environmental interactions
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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

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Ecosystems – Species Diversity & Environmental Interactions

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Ecosystems species diversity environmental interactions

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

Learning Targets:

Natural selection

How evolution influences biodiversity

Reasons for species extinction

Ecological organization

Population characteristics

Population ecology

Conserving biodiversity

Organisms and species

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

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

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 selection

Evolution by natural selection

  • Micro-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 mostinformative concepts in all science

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

    • Both, Darwin andWallace 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

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

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 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 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

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

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

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



Speciation 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

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


Bird dances: rifle bird ; moonwalk.

Speciation results in diverse life forms

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

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 = 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

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

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. amphibian species are vulnerable

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

  • 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

Striking gold in costa rica

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

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