Download Community Ecology Chapter 54

Community Ecology Chapter 54
A community is an interaction between individuals of different species at a place living close enough to have
potential interactions. A Habitat is the place where the community lives.
1. Interspecific interactions are between organisms of different species in a community. Examples include
Competition, Predation, and Symbiosis. Community interactions are classified by whether they help, harm,
or have no effect on the species involved.
2. Interspecific interactions can affect the survival and reproduction of each species, and the effects can be
summarized as positive (+), negative (−), or no effect (0).
3. Competition: Interspecific competition (−/− interaction) occurs when species compete for a resource in
short supply
4. Competitive Exclusion: Strong competition can lead to competitive exclusion, local elimination of a
competing species
5. The competitive exclusion principle states that two species competing for the same limiting resources
cannot coexist in the same place
6. Ecological Niches and Natural Selection: The sum of a species’ use of biotic and abiotic resources is called
the species’ ecological niche
7. An ecological niche can also be thought of as an organism’s ecological role
8. Ecologically similar species can coexist in a community if there are one or more significant differences in
their niches
9. Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a
community.
10. Character displacement is a tendency for characteristics to be more divergent in sympatric populations of
two species than in allopatric populations of the same two species. It reduces interspecific competition for
similar resources.
11. An example is variation in beak size between populations of two species of Galápagos finches
12. Predation (+/− interaction) refers to an interaction in which one species, the predator, kills and eats the
other, the prey
13. Some feeding adaptations of predators are claws, canines, fangs, and poison.
14. Mimicry: In some cases, a prey species may gain significant protection by mimicking the appearance of
another species
15. In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model
16. In Müllerian mimicry: Two unpalatable species mimic each other. For example Yellow jacket and Cuckoo
bee.
17. Herbivory (+/− interaction) refers to an interaction in which an herbivore eats parts of a plant or alga
18. It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores
19. Symbiosis is a relationship where two or more species live in direct and intimate contact with one another
20. In parasitism (+/− interaction), one organism, the parasite, derives nourishment from another organism, its
host, which is harmed in the process
21. Parasites that live within the body of their host are called endoparasites
22. Parasites that live on the external surface of a host are ectoparasites
23. Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction
that benefits both species. For example, an alga and a fungus partners in a lichen.
24. In commensalism (+/0 interaction), one species benefits and the other is neither harmed nor helped
25. Facilitation (+/+ or 0/+) is an interaction in which one species has positive effects on another species
without direct and intimate contact
26. For example, the black rush makes the soil more hospitable for other plant species
27. Diversity of a community means the species richness and their relative abundance.
28. Species richness is the number of different species in the community
29. Relative abundance is the proportion each species represents of all individuals in the community
30. Diversity and Community Stability: greater the diversity of species the higher is the stability of the
community.
a. More productive; they produce more biomass (the total mass of all organisms).
b. Better able to withstand and recover from environmental stresses
c. More resistant to invasive species, organisms that become established outside their native range
31. Trophic structure is the feeding relationships between organisms in a community
32. It is a key factor in community dynamics
33. Food chains link trophic levels from producers to top carnivores
Communities have different food chains linked by predation. Each level is called a trophic level. These always
start with Autotrophs = producers that use the sunlight to make their food.
Top Carnivore = tertiary consumer, lion
Carnivore = Secondary consumer, human, cheetah, tiger
Herbivore = primary consumer, deer, hare, zebra, antelope
Producers = autotrophs, grass, plants
4th trophic level
3rd trophic level
2nd trophic lelvel
1st trophic level
34. Prevalent forms of plants in a community mainly determine the type of animals living in that community.
35. The dead bodies of each level are degraded into simple chemicals by Decomposers = Detrivores
36. Some animals like earthworms, millipedes and many larvae are Detrivores because these feed on dead
matter.
37. Bacteria, slime molds and fungi are important decomposers
38. The different organisms like grass or plants, deer or antelope, cheetah or tiger present on same trophic level
do not eat each other and are called Competitors.
39. The organisms feeding on different trophic levels like humans are called Omnivores. Humans feed directly
on plants and animals.
40. Food Chain is linear and joined by predation. Grass  Deer  Lion
41. Omnivore feeds at more than one trophic levels – bears, humans
42. Detrivores feed on detritus, a partially decomposed plant or animal part.
43. Food Web has many interconnected food chains. Only food webs exist in nature
44. A food web is a branching food chain with complex trophic interactions
45. Species may play a role at more than one trophic level
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Each food chain in a food web is usually only a few links long (mostly not more than 6).
Dominant species are those that are most abundant or have the highest biomass
Keystone species exert strong control on a community by their ecological roles, or niches
In contrast to dominant species, they are not necessarily abundant in a community
Field studies of sea stars illustrate their role as a keystone species in intertidal communities
Sea otters feed on sea urchins and prevent them from overcrowding and keep kelp forests stable.
Ecosystem engineers (or “foundation species”) cause physical changes in the environment that affect
community structure
For example, beaver dams can transform landscapes on a very large scale
A disturbance is an event that changes a community, removes organisms from it, and alters resource
availability.
Disturbance of Communities, when moderate in severity and occurrence leads to increase in diversity of
species in the community. Disturbance usually leads to Ecological Succession.
Ecological Succession is Primary when it starts on bare wood, sand or rock with no soil. For example, rocks
exposed by receding glaciers in Alaska. It takes hundreds of years to reach climax community. Disturbances
like hurricanes, fires eliminate the community but leave the soil intact – The Succession is called Secondary,
it takes lesser time to reach climax community.
For example, abandoned agricultural land may return to its original state through secondary succession
Human Disturbance: Humans have the greatest impact on biological communities worldwide
Both terrestrial and marine ecosystems are subject to human disturbance
Human disturbance to communities usually reduces species diversity
Latitudinal Gradients: Species diversity in a community falls along an equatorial (0˚) to polar (90˚) gradient.
Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and
climate
Temperate and polar communities had to start time and again after glaciations (ice age) and tropical
communities have been stable for long periods.
Growing season is limited in temperate or polar communities but tropical communities have longer growing
season.
Climate is likely the primary cause of the latitudinal gradient in biodiversity
Two main climatic factors correlated with biodiversity are sunlight and precipitation
Can be studies together by measuring a community’s evapotranspiration.
Evapotranspiration is evaporation of water from soil plus transpiration of water from plants
Pathogens, disease causing organisms, alter community structure locally and globally.
Pathogens can have dramatic effects on communities
For example, coral reef communities are being decimated by white-band disease