Ecology

Copyright © 2005

Biology A

Biodiversity and Natural Selection

Biodiversity

• Biodiversity is the sum total of different kinds or organisms..
• The species is the basic unit by which we measure biodiversity.

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• A comparison: If every store in Westport was a bakery, it would not be a successful (profitable) town. By having diversity – clothes stores, shoes, food, office supplies, Westport is successful (and profitable).

E. coli bacterium

Biodiversity

• Organisms have adaptations to exploit, to varying extents, the resources in their habitat.
• Where resource competition is intense, adaptations enable effective niche specialization and partitioning of resources.
• In the African savanna, grazing and browsing animals exploit different food resources within the same area or even within the same type of vegetation.

• Different species have different strategies to obtain

energy. For example Biodiversity is the sum of these

strategies.

African Browsers 1

• An Oryx can only browse the lowest acacia branches, less than 1 m above the ground. Their small pointed muzzles avoid the hooks and spines that defeat clumsier browsers.
• Impalas, with their larger muzzles and longer necks, can reach three times higher than the Oryx.

Oryx

30.5-40.5 cm at shoulder

3-7 kg

Impala

80-90 cm at shoulder

40-65 kg

African Browsers 2

• The disproportionately small head of the gerenuk allows it to browse between the thorny branches. Swiveling hip joints allow it to stand erect and reach taller branches.
• Giraffes browse the upper branches of the acacia.�Its long (45 cm) muscular tongue is impervious to thorns and its long neck is so mobile that its head can tip vertically.

Gerenuk

90-105 cm at shoulder

28-52 kg

Giraffe

3.3 m at shoulder

6 m to crown

0.6-1.9 tonne

Competition in Eucalyptus

• In the eucalyptus forests of eastern Australia different bird species forage at different heights in the forest.
• This selective foraging behavior reduces competition.

Mangrove Adaptations�Some plants need to live in dry areas and others can live in very wet areas

Water level at high tide

Natural Selection

Natural selection provides the following mechanism for evolution: Some variation in heritable characteristics exists within every species; some of these characteristics give individuals an advantage over others in surviving and reproducing; and the advantaged offspring, in turn, are more likely than others to survive and reproduce. As a result, the proportion of individuals that have advantageous characteristics will increase.

The Concepts of Natural Selection

• Darwin’s view of life was of ‘descent with modification’:

present day species are modified descendents of their ancestors

• The mechanism for adaptation is called ‘natural selection’, and is based on a number of principles:
• Overproduction
• Variation
• Competition
• Survival & reproduction of the fittest
• Favorable combinations increase

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Natural Selection is a major cause in biodiversity

The Concepts of Darwinism

• Darwin’s view of life was of ‘descent with modification’:�descendants of ancestral forms adapted to different environments over a long period of time.
• The mechanism for adaptation is called ‘natural selection’, and is based on a number of principles:
• Overproduction: Species produce more young than will survive to reproductive age (they die before they have offspring).
• Variation: Individuals vary from one another in many characteristics (even siblings differ). Some variations are better suited then others to the conditions of the time.
• Competition: There is competition among the offspring for resources (food, habitat etc.).
• Survival & reproduction of the fittest: The individuals with the most favorable combinations of characteristics will be most likely to survive and pass their genes on to the next generation.
• Favorable combinations increase: Each new generation will contain more offspring from individuals with favorable characters than those with unfavorable ones.

Natural Selection Provides the following mechanism for evolution:

• Some variation in heritable characteristics exists within every species; some of these characteristics give individuals an advantage over others in surviving and reproducing.
• The offspring with the advantageous trait will be more likely to survive and reproduce, and as a result, the proportion of individuals that have advantageous characteristics will increase.

http://scienceaid.co.uk/biology/ecology/images/mothevolution.png

Natural Selection Provides the following mechanism for evolution:

Lightly colored peppered moths were frequently seen in England before the Industrial Revolution, however, as a result of the growing industry, the lightly colored tress on which they lived became covered with soot and turned dark. Over the next few generations, the dark phenotype became more frequently seen in the English peppered moth population.

http://scienceaid.co.uk/biology/ecology/images/mothevolution.png

Natural Selection Provides the following mechanism for evolution:

• Changes in the environment (natural disasters, climate change, humans, new species or the removal of species) will lead to organisms that are well suited for a particular environment.
• Fitness a measurement of an individuals ability to survive and reproduce, scientists can measure an organisms fitness based on the number of viable offspring it produces.

http://www.mothcount.brc.ac.uk/images/600x450/Peppered%20Moths%20normal%20and%20melanic%20(Chris%20Manley).jpg

Natural Selection

Changes in the Environment

• Changes in the habitat or ecosystem can impact biodiversity positively or negatively. These changes can be:

• Disturbances
• Climate change
• Species dynamics
• Humans

• Tropical deforestation results in considerable loss of biodiversity and contributes to global warming through a large reduction in net photosynthesis (loss of carbon sinks).

Bulldozer at work, Solomon Islands

Selective Pressures

Slower, more vulnerable individuals are often those that fall prey to predators

Natural selection favors the more capable hunters

• Selective pressures can influence the selection of a trait

Selective pressure is any phenomena which alters the behavior and fitness of living organisms within a given environment. It is the driving force of evolution and natural selection, and it can be divided into two types of pressure: biotic or abiotic

�For example: Predation provides strong selective pressure on prey populations to evolve effective defense mechanisms, e.g.…

• greater speed and agility
• better surveillance

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