Chapter 4 Ecosystems and Living Organisms

I. Evolution

• A. The cumulative genetic changes that occur in a population of organisms over time

– 1. Current theories proposed by Charles Darwin, a 19th century naturalist

– 2. Occurs through natural selection

• B. Natural Selection

– 1. Individuals with more favorable genetic traits are more likely to survive and reproduce

– 2. Frequency of favorable traits increase in subsequent generations

II. Natural Selection

• A. Based on four observations about the natural world:

1. High Reproductive Capacity – each species produces more offspring than will survive to maturity

2. Heritable Variation – the individuals in a population exhibit variation – some traits improve the chances of an individual’s survival and reproductive success, whereas others do not

3. Limits on Population Growth, or a Struggle For Existence – only so much food, water, light, space, etc. are available to a population so organisms compete with one another – not all will survive – also includes predators and disease

4. Differential Reproductive Success – individuals that possess the most favorable combination of characteristics are most like to survive, reproduce, and pass their traits to the next generation

• B. Darwin’s finches exemplified the variation associated with natural selection

III. The Modern Synthesis

• A. An attempt to explain variation among offspring (mutation)

– 1. Includes knowledge from genetics, classification, developmental biology, fossils and ecology

Domains of Life

IV. Biological Communities

• A. Communities vary greatly in size and lack precise boundaries – 1. They are often nestled within each other

• B. Oak Forest Community Relationships

– Possible to link lyme disease to bumper acorn crops

V. Ecological Niche

• A. The totality of an organisms adaptations, its use of resources, and the lifestyle to which it is fitted

• B. Takes into account all aspect of an organisms existence

– 1. Physical, chemical, biological factors needed to survive

– 2. Habitat

– 3. Abiotic components of the environment

• C. Fundamental niche

– 1. Potential idealized ecological niche

• D. Realized niche

– 1. The actual niche the organism occupies

• Ex: Green Anole and Brown Anole

Green Anole and Brown Anole Fundamental niches of 2 lizards initially overlapped Brown anole eventually out-competed the green anole, thereby reducing the green anole’s realized niche

VI. Limiting Resources

• A. Any environmental resource that, because it is scarce or at unfavorable levels, restricts the ecological niche of an organism

• B. Competition

– 1. Interaction among organisms that vie for the same resource in an ecosystem

– 2. Intraspecific

• a. Competition between individuals in a population

– 3. Interspecific

• a. Competition between individuals in 2 different species

Interspecific Competition

• C. Competitive Exclusion & Resource Petitioning

– 1. Competitive Exclusion • a. One species excludes another from a portion of the same niche

as a result of competition for resources

– 2. Resource Partitioning (below) • a. Coexisting species’ niche differ from each other in some way

VII. Symbiosis

• A. An intimate relationship between members of 2 or more species

– 1. Participants may be benefited, harmed or unaffected by the relationship

– 2. Result of coevolution – coevolution is the interdependent evolution of two interacting species

• Example: flowering plants and their animal pollinators

• B. Three types of symbiosis – A. Mutualism - Symbiotic relationship in which

both members benefit • Ex: Mycorrihzal fungi and plant roots

– Fungus provides roots with unavailable nitrogen from soil

– Roots provide fungi with energy produced by photosynthesis in the plant

Left: root growth without fungi

Right: root growth with fungi

• B. Commensalism - Symbiotic relationship where one species benefits and the other is neither harmed nor helped

– Ex: epiphytes and tropical trees

Epiphytes uses tree as anchor

Epiphyte benefits from getting closer to sunlight, tropical tree is not affected

• C. Parasitism - Symbiotic relationship in which one species is benefited and the other is harmed

– Parasites rarely kill their hosts

Ex: ticks

Ticks attach themselves to skin of animals and consume their blood

VIII. Predation

• A. The consumption of one species by another

• B. Many predator-prey interactions

– 1. Most common is pursuit and ambush

• C. Plants and animals have established specific defenses against predation through evolution

• D. Pursuit - Pursuing prey- chasing prey down and catching it

– Ex: Day gecko and spider (below)

• E. Ambush- predators catch prey unaware

– Camouflage

– Attract prey with

colors or light

• E. Plant Defenses Against Herbivores

– 1. Plants cannot flee predators

– 2. Adaptations

• a. Spikes, thorns, leathery leaves, thick wax

• b. Protective chemicals that are poisonous or unpalatable

• F. Defensive Adaptation of Animals – 1. Fleeing or running

– 2. Mechanical defenses • Ex: quills of porcupines, shell of turtles

– 3. Living in groups

– 4. Camouflage

– 5. Chemical defenses - poisons • Ex: brightly colored poison

arrow frog

IX. Keystone Species

• A. A species that exerts profound influence on a community

– 1. More important to the community than what would be expected based on abundance

• B. The dependence of other species on the keystone species is apparent when the keystone species is removed

– 1. Protecting keystone species is a goal to conservation biologists

X. Species Richness

• A. The number of species in a community – 1. Tropical rainforests =

high species richness

– 2. Isolated island = low species richness

• B. Related to the abundance of potential ecological niches

XI. Ecosystem Services

• A. Important environmental benefits that ecosystems provide, such as:

– 1. Clean air to breathe

– 2. Clean water to drink

– 3. Fertile soil in which to grow crops

XII. Community Development

• A. Succession: the process where a community develops slowly through a series of species

– 1. Earlier species alter the environment in some way to make it more habitable by other species

– 2. As more species arrive, the earlier species are outcompeted and replaced

• B. Two types of succession

– 1. Primary Succession - Succession that begins in a previously uninhabited environment

• a. No soil is present – Ex: bare rocks, cooled lava fields, etc.

• B. General Succession Pattern – Lichen secrete acids that crumble the rock (soil begins to

form)

Lichen mosses grasses shrubs forests

Primary Succession

1. Bare rock with lichen

2. Grasses and shrubs

3. Forest community

1 2

3

Secondary Succession

• C. Secondary Succession - Succession that

begins in an environment following

destruction of all or part of the earlier

community

– Ex: abandoned farmland, open area after fire

– 1. Generally occurs more rapidly than primary

succession

Secondary Succession of an abandoned farm field in North Carolina