Chapter 4! Evolution, Biological Communities, and Species

Interactions

Tolerance Limits

• Includes environmental factors– Temperature– Moisture levels– Nutrient supply– Soil/Water chemistry– Living space

• Environmental Indicators- organisms/physical factors that serve as a gauge for environmental changes

Evolution

• Four conditions:– Different traits must be present– These traits must affect reproductive success– Traits must be genetic– Selective pressure must favor these traits

differently

• Mutations- random changes in DNA; only affects evolution if they occur in the gametes

Selective Pressure

• Organisms can be subjected to artificial pressure

• Selection can be a positive or negative force• Resource Partitioning- various populations

sharing environmental resources through specialization; thereby reducing direct competition

• Radiative Evolution- divergence from a common ancestor into two or more new species

Isolation

• Reproductive isolation prevents gene flow• Types of isolation:

– Geographic– Mechanical– Temporal– Behavioral– Ecological

Ecological Niches• Niche- description of the role played by a species or the

set of environmental factors that determine species distribution

• Generalists vs. Specialists• Genetic vs. Social• Law of Competitive Exclusion-no two species will occupy the same niche and compete for the same resources in thesame habitat for long

Predators

• Feed directly upon living organisms, regardless of whether or not they killed it

• Feeding targets change as the predators mature

• Force evolution on other species= coevolution

• Parasites- feed on hosts without killing them

• Pathogens- disease-carrying organisms

Keystone Species

• A group of species whose impacts on a community are larger than they appear

• Not just top predators• Species are intricately

connected in biologicalcommunities, so it is difficult to determine

the essential key

Competition

• Intraspecific vs. interspecific• Most species avoid a fight• Many species have ways to minimize

competition• Territoriality depends on the size of

species and resources available

Symbiosis

• The intimate living

together of two or

more different species• Enhances survival of

the partners, entails

some degree of

coadaption

Defense• Toxic chemicals and body armor, often

with a bright coloring or distinctive pattern to warn enemies

• Batesian and Müllerian mimicry• Camouflage is another way organisms

defend themselves from predators.

Productivity

• Primary productivity is the rate of biomass production

• Rates are regulated by: light levels, temperature, moisture, nutrient availability

• Only a small percentage of the sunlight available is ever absorbed

Abundance and Diversity• Abundance is an expression of the total

number of organisms in a biological community

• Diversity is a measure of the number of different species or genetic variations present

• Abundance and diversity are inversely related

• Dependent on the total resource availability, resource reliability, adaptations of the species, and interactions between species

Community Structure• Ecological structure is the

patterns of spatial distribution

of populations in an area• Individuals live where resources

are available and can be distributed

randomly• Species cluster together for

protection, assistance, reproduction,

or access to an environmental resource

Complexity and Connectedness

• Complexity refers to the number of species at each trophic level

• Diverse communities might not be complex if all the species are in a few trophic levels

• Highly connected communities generally have more trophic levels

Resilience and Stability

• Three types of resilience:– Constancy: lack of fluctuations in composition

or function– Inertia: resistance to perturbations– Renewal: ability to repair damage after

disturbance

Edge Effects

• The boundary between one habitat and its neighbors

• Community sharply divided is a closed community while one where species can cross the borders are open

Ecological Succession• The process by which organisms occupy a site

and gradually change environmental conditions• Follows an orderly sequence of events• Climax community is the culmination of the

successional process and resists further change

Primary Succession

• Occurs when a community begins to develop on a site previously unoccupied by living organisms

• Pioneer species start the cycle of living organisms and are replaced as the environment changes and new species emerge

Secondary Succession

• Occurs when an existing community is destroyed and a new one takes its place

• Starts with pioneer species, which are again replaced as the environment changes and the site becomes richer

Equilibrium Communities

• These are communities that never reach a stable climax because they are characterized by and adapted to periodic disruption– Fire-climax communities are maintained by

periodic fires and their structure would be skewed without them

Invasive Species• Succession requires the continual introduction of new

species as old ones die out• Introduced species may prey on or compete more

successfully with native species, sometimes causing the entire community to change

• Humans try to introduce new species in an attempt to solve problems created by other organisms, but these often make the situation worse

Kudzu in Alabama

Case Study #1-Burmese Pythons• First Burmese python appeared in the Everglades National

Park (Florida) in the 1990’s• Causes:

– People who buy them as 20-inch babies can not take care of them when they grow to 12 feet and release them into the wild

– Hurricane Andrew in 1992 destroyed an exotic snake warehouse

• The climate was similar to the warm climate of Asia (their native home), the thick vegetation was favorable to the snakes

• Little to no predation causes the python population to boom and become a serious threat to the native species the park is trying to protect

• In the past ten years, 1,300 Burmese pythons have been captured for research on how to eradicate the pests

• What’s being done about it:– On Non-Native Amnesty Day, the Florida Fish and Wildlife Conservation

Commission encourages owners of unwanted exotic pets to turn them in to zoos and such

– Senator Bill Nelson has proposed legislation to make the importing of many exotic snakes illegal

Case Study #2-Natural Selection

• Poecilia reticulata, also known as guppies, have varying average age and size of sexual maturity based on what pool along the Aripo River on the island of Trinity they are found in

• The variation was correlated with the difference in primary predators in each pool: – Small killifish prey on juvenile guppies– Larger pike-cichlids prey on mature guppies

• Scientists noticed that the guppies in the pools dominated by pike-cichlids tend to be younger and smaller at maturity

Case Study #2 Cont.• To ensure that the predation differences were

causing the selection, the scientists transplanted fish from the pike-cichlid dominated pools to pools containing only killifish

• Results over 11 years:– After 30-60 generations, the transplanted fish were an

average of 14% heavier at maturity than the guppies that were left in their original pools

• Conclusion:– The pike-cichlids prey mainly on larger, adult guppies,

and therefore the chance of growing to maturity and reproducing is low

– The guppies that reached sexual maturity at a younger age and a smaller size survived to pass on their genes

– Natural selection favored these fish and the general population became more like the ideal guppies

The end