1. Community Ecology
Chapter 8

2. COMMUNITY STRUCTURE AND SPECIES DIVERSITY
Biological communities differ in their structure or spatial distribution.
Figure 7-2

3. Community Structure has 4 characteristics:
1. Physical appearance: relative size, stratification & distribution of its populations and species
2. Species diversity or richness
3. Species abundance
4. Niche structure – number of ecological niches, species interactions with similarities and differences

4. Species Diversity and Niche Structure: Different Species Playing Different Roles
Biological communities differ in the types and numbers of species they contain and the ecological roles those species play.
Species diversity: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness).

5. Species Diversity and Niche Structure
Niche structure: how many potential ecological niches occur, how they resemble or differ, and how the species occupying different niches interact.
Geographic location: species diversity is highest in the tropics and declines as we move from the equator toward the poles.

6. What determines species diversity ?
Edge Effect-the boundaries between two ecosystems (ecotones) may have a
different combination of species than those
found in the two ecosystems.
Forest-field ecotone and game species
The most species rich areas:
Coral reefs
Large tropical lakes

7. Three main factors affect species diversity:
1. Latitude – decreases as moves away from equator

8. 2. Depth in aquatic systems – increases from surface to 2000 m, then decreases until the sea bottom where diversity is usually high

9. 3. Pollution in aquatic systems

10. Case Study: Species Diversity on Islands
MacArthur and Wilson proposed the species equilibrium model or theory of island biogeography in the 1960’s.
Model projects that at some point the rates of immigration and extinction should reach an equilibrium based on:
Island size
Distance to nearest mainland

11. TYPES OF SPECIES
Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities.
Native: those that normally live and thrive in a particular community.
Nonnative species: those that migrate, deliberately or accidentally introduced into a community.

12. Indicator Species: Biological Smoke Alarms
Species that serve as early warnings of damage to a community or an ecosystem.
Presence or absence of trout species because they are sensitive to temperature and oxygen levels.
Canary in the Coal mine – they sang untill increase in CO
Salmon and Stoneflies
Amphibians

13. Case Study: Why are Amphibians Vanishing?
Frogs serve as indicator species because different parts of their life cycles can be easily disturbed.
Figure 7-3

14. Case Study: Why are Amphibians Vanishing?
Habitat loss and fragmentation.
Prolonged drought.
Pollution.
Increases in ultraviolet radiation.
Parasites.
Viral and Fungal diseases.
Overhunting.
Natural immigration or deliberate introduction of nonnative predators and competitors.

15. Keystone Species-
Strong interaction with other species affect the health and survival of the
other species. Significance is out of proportion with their biomass…. In other words, a small biomass of these organisms have a large effect on the ecosystem.
Pacific Northwest Millipede
They process material
out of proportion to
their numbers or
biomass

16. Top Predators-
Interaction Between Species
Intraspecific Competition-
Territoriality-
Interspecific Competition-
Interference Competition-
Exploitation Competition

17. The Competitive Exclusion Principle
Says that two species sharing the same Resource cannot coexist indefinitely in an ecosystem that does not have enough resources to meet the needs of both species.

18. Strategies that Reduce Competition
Resource Partitioning- share the wealth by using a resource at
Different times
In different ways
In different places
Fundamental verses Realized
Niche
Hawks and Owls
Lions and Leopards
Chum and Coho Salmon

19. Predator-Prey Relationships
On the population level predators are beneficial to prey
because the predator
Reduces the prey population giving remaining
prey greater access to the available food supply
Improve the genetic stock of the prey population
Examples of predator adaptations that maximize their
chances of getting a meal
Cheetahs-speed
Eagles
Wolves and Lions-teamwork
Snowy Owls

20. PREDATION Some prey escape their predators or have outer protection:
Mimicry
Deceptive Looks
Deceptive Behavior
Warning Coloration
Camouflaged
Chemicals warfare to repel predators.
Figure 7-8

21. Symbiotic Relationships
Parasitism- one benefits while the other is harmed (host) Usually draws nutrients from the host which weakens it, but seldom kills it.
Some parasites live inside (tapeworm); others live outside (fleas and mosquitoes)

22. Mutualism: Win-Win Relationship
(a) Oxpeckers (or tickbirds) feed on parasitic ticks that infest large, thick-skinned animals such as the endangered black rhinoceros.
(b) A clownfish gains protection
& food by living among deadly
stinging sea anemones and helps
protect the anemones from some
of their predators.
(c) Beneficial effects of mycorrhizal fungi attached to roots of juniper seedlings on plant growth compared to
(d) growth of such seedlings in sterilized soil without mycorrhizal fungi.
Figure 7-9

23. Mutualism-both benefit
Lichens are a relationship between a
fungus and an algae. The fungus supplies _________ and receives___________ from the algae. The algae supplies ____________ and receives ___________ from the fungus
Rhizobium bacteria and the roots of legumes
Zooanthellae and coral polyps
Clownfish and sea anemones
Mycorrhizae fungi and the roots
of many trees

24. Commensalism: Using without Harming
Some species interact in a way that helps one species but has little or no effect on the other.
Figure 7-10

25. Ecological Succession –gradual change in species composition in a specific area.
1. Primary succession – establishing life on lifeless ground
Begins where there is no soil in terrestrial ecosystems
no bottom sediment in aquatic ecosystems
Pioneer species start things off by getting a foothold on bare surfaces like rocks. Lichens and moss specialize at this.
They secrete acids which begin to breakdown the rock and they trap wind blown soil and bits of organic matter.

26. Primary Succession: Starting from Scratch
Primary succession begins with an essentially lifeless are where there is no soil in a terrestrial ecosystem
Figure 7-11

27. Early successional plant species follow. Typically these:
Grow close to the ground
Grow quickly under harsh conditions
Have short lives
Ex: include small perennial grasses, herbs, or ferns
Mid-successional species follow these which include less hardy species of grasses, herbs, and low shrubs
Late successional species are typically those that are adapted to the climate and soil type of the area and are typically trees

28. Secondary succession-begins in areas where an established natural community has been disturbed
Abandoned farmlands
Burned or cut forests
Heavily polluted streams
Land that has been dammed or flooded

29. Secondary Succession: Starting Over with Some Help
Secondary succession begins in an area where the natural community has been disturbed.
Figure 7-12

30. Three species interactions involved in succession
1. Facilitation- one species makes an area suitable for another species with different niche requirements. Example… lichens, legumes & N
2. Inhibition- early species hinder the establishment and growth of other
species. Example… plants that release toxins
3. Tolerance- late successional stages are unaffected by earlier successional
stages. Example…

31. Disturbances and species diversity
Intermediate disturbance hypothesis -
communities that experience fairly frequent,
moderate disturbances have the greatest species diversity
Old View of Succession
Orderly progression of successional stages building towards a stable community of a few long lived species known as a ______________ community.
Instead, most disturbed communities result in ever-changing mosaic of vegetation patches at different successional stages.

32. ECOLOGICAL STABILITY AND SUSTAINABILITY
Living systems maintain some degree of stability through constant change in response to environmental conditions through:
Inertia (persistence): the ability of a living system to resist being disturbed or altered.
Constancy: the ability of a living system to keep its numbers within the limits imposed by available resources.
Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance.

33. ECOLOGICAL STABILITY AND SUSTAINABILITY
Having many different species appears to increase the sustainability of many communities.
Human activities are disrupting ecosystem services that support and sustain all life and all economies.

34. The Precautionary Principle
When evidence indicates that our actions may harm the environment, even though all the “cause and effect” relationships have not been established
between our actions and harm to the environment, it is better to take precautionary measures to prevent harm.
It is easier to prevent pollution than it is to clean it up once the harm of that pollution has been established.
It is easier to protect ecosystems than it is to recreate them once they have been destroyed.
How much time and effort should we put into preventing Global Warming
when we are not even sure of the ultimate effects of climate change ?