1. Chapter 6
Community Ecology,
Population Ecology,
& Sustainability

2. Community Structure
Structure of a community (populations of all species living and interacting in an area at a particular time)
Physical appearance: relative size, stratification & species distribution
Species diversity: # of different species
Species abundance: # of individuals of each species
Niche structure: number of niches, how they differ & how they interact

3. Physical Appearance
Differences in physical structure and properties create transition zones between 2 ecosystems (ecotones)
Edge effect: area between forest and grasslands
Many animals and plants thrive “on the edge”
Many species can become stressed in the edge as well

4. Species Diversity & Abundance
Most of the Earth’s diversity is in the rainforest, coral reefs, deep sea & large tropical lakes
Large amount of diversity = low number of organisms of a particular type (abundance)
Three major factors effect diversity
Latitude in terrestrial communities
Depth in aquatic zones
Pollution in aquatic communities

5. Niche Structure Niche is analogous to its job
Ecological niche represents the adaptations or adaptive traits through evolution
Fundamental niche: full potential range if there is no competition for resources
Realized niche: occupies only part of its fundamental niche
Generalist species have broad niches
Specialized species have narrow niches

6. Types of Species Native – normally live in an ecosystem
Non-native – (invasive or exotic) deliberately or accidentally introduced into an ecosystem
Indicator – serve as early warning signs for damage or pollution of an ecosystem
Keystone – play a critical ecological role by effecting the type and abundance of other species
Foundation – enhance a habitat to benefit other species

7. Species Interaction
Interspecific competition– competition between species for food & resources
Resource partitioning – adapt to reduce competition (hawks & owls)
Predation – one species (predator/hunter) lives off of another species (prey/hunted)
Parasitism – one species (parasite) lives on another species (host)
Mutualism – two species live together to benefit both
Commensalism – one species benefits, but the other is not harmed

8. Ecological Succession
All communities and ecosystems change constantly
Ecological succession – gradual change in species composition
Primary succession: biotic communities in an abiotic environment
Secondary succession: biotic communities in an biotic environment

9. Primary Succession See figure 6-9 on page 119.
Begins in a lifeless area where there is no soil or bottom sediment (bare rocks, parking lots, cooled lava, etc.
Lichens & mosses build up soils
Early successional plant species (herbs & grasses) grow fast & have short lives
Mid-successional plant species (shrubs & trees)
Late successional plant species (trees that can tolerate shade) becomes a complex forest community

10. Secondary Succession See figure 6-10 on page 120.
Begins in an area that has soil and was previously a community of organisms
New vegetation can grow due to winds carrying seeds, or animal droppings
Secondary succession includes
Abandoned cropland
Burned or cut forests
Heavily polluted streams, ponds or lakes
Land that has been dammed or flooded

11. Disturbances Changes in the environment that disrupts the ecosystem
Catastrophic or mild
Natural or caused by humans
Detrimental or beneficial
Intermediate disturbance hypothesis predicts that communities that experience frequent but moderate disturbances have the most species diversity

12. The Balance of Nature?
Climax community: dominated by few long-lived plant species and is at equilibrium
Ever-changing mosaic vegetation patches at different stages of succession
We can not predict the course of succession toward an ideal climax community

13. Population Change Four variables
Birth
Death
Immigration
Emigration
Population change = (birth + immigration) – (deaths + emigration)

14. Limits on Population Growth
Biotic potential – capacity for growth
Intrinsic rate of increase (r) – rate of growth if there were unlimited resources
Environmental resistance – all factors that act together to limit growth
Carrying capacity (K) – the result of biotic potential and environmental resistance
Minimum Viable Population (MVP) – certain minimum population required to sustain its growth

15. Exponential vs Logistic
Exponential growth starts small increasing ever so rapidly (J shaped)
Logistic growth starts slow, increases for a time and then levels off (S shaped)
Overshoot – an initial spike followed by a decline in population (reproduction time log)
Carrying capacity – population becomes a constant (at equilibrium)

16. Predation In Population Control
Top-down control: predator periodically reduces the population of prey, which then reduces the population of the predator, which in turn allows the prey population to increase again
Bottom-up control: periodic population crashes influence the food supply

17. Reproduction & Survival
Asexual reproduction – clones of their parents
Sexual reproduction – requires genetic information from 2 parents
Provides greater genetic diversity
Allows the males to gather food & help raise the young

18. Reproductive Patterns
K-selected species are competitors
Many offspring each time they reproduce
Early reproductive rate
High potential growth rate
R-selected species are opportunists
Born live, mature slowly & cared for by parent
Do well in competitive situations
Low reproductive rates
Thrive best in constant environments

19. Human Impacts on Ecosystems
Reduced biodiversity by destroying, fragmenting, degrading & simplifying wildlife habitats
Used, wasted, and destroyed an increasing percentage of Earth’s net primary productivity
Strengthened some populations of pests and disease causing bacteria and viruses
Eliminated some predators
Deliberately or accidentally introduced non-native species into communities

20. Human Impacts (cont.)
Used some renewable resources faster than we can replenish
Interfere with the normal chemical cycling and energy flows in ecosystems
Become increasingly dependent on nonrenewable energy sources – fossil fuels – which have a whole host of global impacts in the extraction, processing, consumption and disposal of waste product generated by the use of fossil fuels

21. Ecosystem Stability Stability is maintained by constant dynamic change
Inertia (persistence) is the ability for organisms to resist change
Consistency is a restriction to change due to limited resources
Resiliency is the ability for organisms to bounce back

22. Sustainability Human aspects can be controlled
Balance of resource usage
Use less and waste less
Alternatives must be utilized
“Going Green”
Strive for sustainable communities

23. Sustainability Lifestyles – we need to change
Connections – we need to be aware of our interdependency with everything else
Intrusion – we need to ask ourselves what happens when we alter nature
Can not continue to deplete & degrade – we need to become more sustainable in all aspects of our lives

24. The Precautionary Principle
It is important to take precaution in activities or behavior that may be harmful to the health of species or the environment.
See figure 6-18 on page 126.