1. Chapter 4! Evolution, Biological Communities, and Species Interactions

2. 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

3. 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

4. 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

5. Isolation Reproductive isolation prevents gene flow
Types of isolation:
Geographic
Mechanical
Temporal
Behavioral
Ecological

6. 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 the
same habitat for long

7. 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

8. 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 biological
communities, so it is
difficult to determine
the essential key

9. 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

10. Symbiosis The intimate living together of two or
more different species
Enhances survival of
the partners, entails
some degree of
coadaption

11. 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.

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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 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

26. The end