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28 Cards in this Set

  • Front
  • Back
Community Ecology
- Composition: how many species and which species
- Trophic network: who is eating whom?
- WHo interacts w/ whome?
- How important is competition and mutualism in determining the composition and trophic network in a community?
- How do communities get started? What happens after disturbance? - succession
54.1 Community Interactions
- INterspecific INteractions: include competition, predation, herbivory, symbiosis, and facilitation

- Predation is a +/- interaction: + effect for predator pop, - effect for prey pop

- 5 types of interactions: competition, predation, herbivory, symbiosis, and facilitation strongly influence structure of communities

- Mutualism: +/+ interaction, survival and reproduction of both species are increased in presence of one another

- 0 indicates that pop is not affected by interaction in any known way
54.1 Community Interactions

- Competition
- Interspecific Competition is -/-
- occurs when individuals of diff species compete for a resource that limits growth and survival
- eg) weeds competing w/ garden plants
54.1 Community Interactions

- Competitive Exclusion
- two species compete for limited resources
- two species competing for same limited resources can't coexist permanently in same place
- one species will use the resources more efficiently and reproduce more rapidly than the other
- eg) Paramecium aurelia, and Paramecium caudatum
54.1 Community Interactions

- Ecological Niches and Natural Selection
- Sum of a species use of abiotic and biotic resources is called Ecological Niche
- Eugen Odum: if an organisms habitat is its addres, the niche is the organisms "profession"
- how it fits into the ecosystem

- competitive exclusion: two species can't coexist permanently in a community if their niches are identical
- differentiation of niches that enables similar species to coexist in a community is called Resource Partitioning

- Fundamental niche, niche potentially occupied by that species is diff from its realized niche, portion of its fundamental niche that it actually occupies.

- testing the range of conditions in which it grows and reproduces in the absence of competition
54.1 Community Interactions

Predation
- +/- interaction, predator kills and eats other prey
- predators have adaptations: claws, teeth, fangs, stingers, poison, ambush disguise

- Prey also have adaptations: hiding, fleeing, forming herds, alarm calls
- Cryptic Coloration, or camouflage makes prey difficult to see
- Mechanical or chemical defense: porcupine, skunks, toxins

- Aposematic Colouration: animals w/ chemical defense exhibit warning colours

- Bastesian Mimicry: prey resemble other species. Harmless prey mimic dangerous predators (hawkmoth larva & green parrot snake)

- Mullerian Mimicry: two or more unpalatable species, cuckoo bee and yellow jacket, resemble each other.

- PRedators also use mimicry. Alligator snapping turtle wags tongue like a worm.
54.1 Community Interactions

Herbivory
+ / - interaction, organism eats part of a plant or alga
- mammalian, invertebrate, and ocean herbivores
- specialized adaptations: insects have chem sensors on feet to distinguish between toxic & non-toxic, sense of smell to examine plants, special teeth & digestive system

- Plants defense: chemical toxins, thorns, spines, poison
54.1 Community Interactions

Symbiosis
two or species live in direct and intimate contact w/ one another
54.1 Community Interactions

Symbiosis: Parasitism
+ / - interaction
- parasite derives nourishment from another organism
- host is harmed in process
- parasites live in body of host (tapeworms) - endoparasites
- parasites feed on external surface (ticks, lice) - Ectoparasites
- 1/3 of all species are parasites
54.1 Community Interactions

Symbiosis: Mutualism
+/+ benefits both species
- flowering plants (nectare, fruit), animals (seed dispersal)
54.1 Community Interactions

Symbiosis: Commensalism
- benefits one of the species, neither harms nor helps other (+/0)
- difficult to document
54.1 Community Interactions

Facilitation
- can have positive effects + / + or 0/+ on survival and reproduction of other species w/out direct contact of symbiosis
- common in plant ecology
(black rush juncus, makes soil more livable for others)
54.2 Diversity and Trophic Structure

SPecies Diversity
- Species Diversity: variety of diff kinds of organisms that make up the community
> has 2 components
1) Species Richness: number of diff species in community
2) Relative abundance: of diff species, proportion each species represents of all individuals in community

- Shannon Diversity (H)
H = - (pA ln pA + pB ln pB + pC ln pC +...)

A,B,C = species in community
p = relative abundance of each species
ln = natural logarithm

- higher value of H = more diverse community
54.2 Diversity and Trophic Structure

Diversity
- Higher-diversity communities are often more resistant to invasive species, which are organisms that become established outside their native range
54.2 Diversity and Trophic Structure

Trophic Structure

- food chain
- Structure and dynamics of a community depend on feeding relationships between organisms - Trophic Structure of the community

- Xfer of food E, up trophic levels from its source in plants (primary producers) through herbivores (consumers) to carnivores (secondary consumers) eventually to decomposers
- Referred to as a food chain
54.2 Diversity and Trophic Structure

Trophic Structure: food webs
- Charles Elton, linked food chains together into food webs

- can be simplified in 2 ways
1) species w/ similar trophic relationships in a given community can be grouped into broad functional groups
2) simplify a food web for closer study is to isolate portion of the web that interacts very little w/ rest of community
54.2 Diversity and Trophic Structure

Trophic Structure: limits on food chain length
- 2 reasons why food chains are short
1) Energetic Hypothesis: length of food chain limited by inefficiency of E transfer along chain

- Biomass: total mass of all individuals in a pop.
(eg: producer - 100 kg of plants can support 10kg of herbivore biomass)

2) Dynamic Stability Hypothesis: long food chains less stable than short chains. Pop. fluctuations.
54.2 Diversity and Trophic Structure

Species w/ a large impact
- are highly abundant
- impact of these species occurs through trophic interaction
54.2 Diversity and Trophic Structure

Species w/ a large impact: Dominant Species
- most abundant
- highest biomass
- exert a powerful control over the occurrence and distribution of other species
- way to discover impact, remove it from community
54.2 Diversity and Trophic Structure

Species w/ a large impact: Keystone species and Ecosystems
- contrast to dominant species, Keystone Species
- not abundant
- strong control on community structure
- not by numerical might, but by pivotal ecological roles or niches
- eg) sea star, maintaining diversity of an intertidal community
- Species that dramatically alter their environment, ECOsystem Engineers
- eg) beaver, could be + or -
54.2 Diversity and Trophic Structure

Species w/ a large impact: Bottom Up & Top Down Controls
- Bottom Up: nutrients (N) > Plant (v) > Herbivore (H) > predator (P)
- about bottom controlling top

- Top down Model: P > H > V > N
- trophic cascade model
eg) top down model to improve water quality in polluted lakes
54.3 Disturbance

- stability, disturbance, nonequilibrium model,
- Stability is a communities tendency to reach and maintain relatively constant composition of species
- F.E Clements: biotic interactions caused the species in this climax community to function as an integrated unit - as a super-organism. - Viewed certain species of plants consistently around each other.

- Disturbance: such as a storm, changes a community by removing organisms from it or altering resource availability

- Non-equilibrium model - describes most communities as constantly changing after being affected by disturbances
54.3 Disturbance

- Characterizing Disturbance
- storms disturb all communities, even ocean
- Fire
- freezing lakes, rivers, ponds
- flooding of streams and ponds
- seasonal drying

intermediate disturbance hypothesis -
- moderate levels of disturbance foster greater species diversity than do low or high levels of disturbance. High levels of disturbance cause environmental stress
54.3 Disturbance

- Ecological Succession
ecological, primary, secondary succession
- Ecological Succession: disturbed area may be colonized by variety of species, gradually replaced by other species, replaced by still other species (continued pattern)

- Primary Succession: virtually lifeless area where soil hasn't formed yet. Only life forms initially present are autotrophic and heterotrophic prokaryotes.

- Secondary Succession: existing community has been cleared by some disturbance that leave soil intact.
54.3 Disturbance

Human Disturbance
- ecological succession is a response to disturbance
- strongest agent of disturbance is human activity: logging, agriculture
54.3 Disturbance

- Latitudinal Gradients
- Charles Darwin & Alfred Wallace: life was more abundant and diverse in the tropics
- 2 key factors in latitudinal gradients of species richness (1) evolutionary history (2) Climate

- Growing season in tropical forests, 5x as long as in tundra. (5x as fast)

- Climate primary latitudinal gradient in richness and diversity
- terrestrial communities, factors correlated w/ diversity are solar E input and water availability

- These factors considered by measuring communities rate of Evotranspiration
> evap of water from soil plus transpiration of water from plants.
54.5 Pathogens alter community structure locally and globally
- Pathogens - disease-causing microorganisms, viruses, viroids,
- pathogens also influence community structure in terrestrial ecosystems
- human activities are transporting pathogens, around the world fast (H1N1)
54.5 Pathogens

- Community Ecology and Zoonotic Diseases
- 3/4 of human disease caused by zoonotic pathogens
- pathogens transferred to humans from animals - direct contact, infected animals , vectors (spread zoonotic disease - parasites, ticks, lice)