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Biological Communities and Species Interaction. Important Concepts:. Critical Environmental Factors Adaptation Natural Selection Speciation Ecological Niche Population Dynamics Community Properties Succession Introduced Species. Types of Species Interactions. Competition

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important concepts
Important Concepts:
  • Critical Environmental Factors
  • Adaptation
  • Natural Selection
  • Speciation
  • Ecological Niche
  • Population Dynamics
  • Community Properties
  • Succession
  • Introduced Species
types of species interactions
Types of Species Interactions
  • Competition
  • Predation – Trophic levels
  • Mutualism
  • Community Structure
  • Succession
critical environmental factors
Critical Environmental Factors
  • Single factor in shortest supply relative to demand is the critical determinant in species distribution.
  • Each environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive.
    • No humans permanently above 5 km
limits of range
Limits of Range
  • Physical Barriers
    • Oceans (humans, cattle egrets, marsupials)
    • Mountains (house finch)
    • Ice (humans in the Americas)
  • Climatic
  • Altitude
  • Food
  • Water
  • Competitors
critical environmental factors1
Critical Environmental Factors
  • For many species, the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution.
    • Altitude = oxygen, temperature, food
    • May be a specific critical factor that mostly determines abundance and distribution.
  • Species requirements and tolerances can also be used as useful indicators.
    • Environmental indicators

Adaptation is used in two ways:

  • Individual (moving from Alabama to Wisconsin)
  • Population (evolution)
natural selection
Natural Selection
  • Natural Selection - Members of a population best suited for a particular set of environmental conditions survive and produce offspring more successfully than their competitors.
    • Acts on pre-existing genetic diversity.
    • Limited resources place selective pressures on a population.
  • Given enough geographical isolation or selective pressure, members of a population become so different from their ancestors that they may be considered an entirely new species.
  • Alternatively, isolation of population subsets, preventing genetic exchange, can result in branching off of new species that coexist with the parental line.
divergent vs convergent evolution
Divergent vs. Convergent Evolution
  • Divergent Evolution - Mutations and different selective pressures cause populations to evolve along dissimilar paths.
  • Convergent Evolution - Unrelated organisms evolve separately to cope with environmental conditions in the same fashion.
    • Look alike - Act alike
    • Usually means some physical basis
ecological niche
Ecological Niche
  • Habitat - Place or set of environmental conditions where a particular organism lives.
  • Ecological Niche
    • Role a species plays in a biological community (e.g. large grassland herbivore)
    • Total set of environmental factors that determines a species’ distribution.
    • Generalists - Broad niche
    • Specialists - Narrow niche
  • When generalists and specialists collide, generalists usually win.
law of competitive exclusion
Law of Competitive Exclusion
  • No two species will occupy the same niche and compete for exactly the same resources for an extended period of time.
  • One will either migrate, become extinct, or partition the resource and utilize a sub-set of the same resource.
  • Given resource can only be partitioned a finite number of times.
  • Feeds directly upon another living organism, whether or not it kills the prey in doing so.
    • Mosquitoes prey on humans
  • Prey most successfully on slowest, weakest, least fit members of target population.
    • Reduce competition, population overgrowth, and stimulate natural selection.
    • Co-evolution (arms race)
co evolution and disease
Co-Evolution and Disease
  • If a disease kills too quickly, it can’t spread
  • Disease can moderate while host becomes more resistant (measles)
  • Disease can be lethal but messy (cholera, ebola)
  • Disease can be lethal but slow-acting (AIDS)
keystone species
Keystone Species
  • Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance.
    • Large predators
    • Critical food organisms (bamboo and pandas)
    • Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.
  • Interspecific - Competition between members of different species.
  • Intraspecific - Competition among members of the same species.
    • Often intense due to same space and nutritional requirements.
      • Territoriality - Organisms defend specific area containing resources, primarily against members of own species.
      • Resource Allocation and Spacing

Intimate living together of members of two or more species.

  • Commensalism - One member benefits while other is neither benefited nor harmed.
    • Cattle and Cattle Egrets
  • Symbiosis - Both members benefit.
    • Lichens (Fungus and cyanobacterium)
  • Parasitism - One member benefits at the expense of other.
    • Humans and Tapeworms
defensive mechanisms
Defensive Mechanisms
  • Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable, dangerous or poisonous species
    • Viceroy and Monarch butterfly
  • Mullerian Mimicry - Two unpalatable species evolve to look alike
    • Bees and Wasps
  • Camouflage
  • Advertising and warning (coral snake)
  • Attracting prey, pollinators, mates, etc.
abundance and diversity
Abundance and Diversity
  • Abundance -Total number of organisms in a community.
  • Diversity - Number of different species, ecological niches, or genetic variation.
    • Abundance of a particular species often inversely related to community diversity.
    • As general rule, diversity decreases and abundance within species increases when moving from the equator to the poles.
  • Primary Productivity - Rate of biomass production. Rate of solar energy conversion to chemical energy.
    • Net Primary Productivity - Energy left after metabolism
    • Highest in rain forest, estuaries, reefs
    • Decreases toward poles
    • Open oceans very low
trophic level food chain
Trophic Level (Food Chain)
  • A pond
    • Phytoplankton
    • Zooplankton
    • Small Fish
    • Larger Fish
    • Higher predators (birds, mammals)
  • Organisms are at same trophic level if they get their food from similar sources
trophic level food chain1
Trophic Level (Food Chain)
  • A forest
    • Decaying organic matter
    • Insects
    • Small mammals and birds
    • Higher predators (owls, foxes, bears)
  • A Pasture or Grassland
    • Grass
    • Herbivore
    • Higher predators
trophic level food chain2
Trophic Level (Food Chain)
  • At each level, some matter goes into biomass
  • Most goes into energy and metabolism
  • Hence each level needs about 10x as much energy, has fewer individuals
  • Bio-Accumulated chemicals get more abundant higher up the food chain
food requirements
Food Requirements
  • Warm-blooded organisms require more food than cold-blooded
    • Predator/prey ratio higher for cold-blooded
    • Indication that some dinosaurs may have been warm-blooded
  • Large organisms eat less in proportion to their mass than small ones
    • Shrew: 100%+ per day
    • Human: 1% per day
improbable movie biology
Improbable Movie Biology
  • Things that eat people (Morlocks, The Time Machine)
  • Really huge carnivores (The Phantom Menace)
  • Huge carnivores in empty environments (Empire Strikes Back, Return of the Jedi)
  • Ultra-voracious carnivores (Jaws, Alien, Anaconda, Jurassic Park)
complexity and connectedness
Complexity and Connectedness
  • Complexity - Number of species at each trophic level, and the number of trophic levels, in a community.
    • Diverse community may not be complex if all species are clustered in a few trophic levels.
    • Highly interconnected community may have many trophic levels, some of which can be compartmentalized.
resilience and stability
Resilience and Stability
  • Constancy (Lack of fluctuation)
  • Inertia (Resistance to pertubation)
  • Renewal (Ability to repair damage)
    • MacArthur proposed complex, interconnected communities would be more stable and resilient in the face of disturbance.
      • Controversial
edges and boundaries
Edges and Boundaries
  • Edge Effects - Important aspect of community structure is the boundary between one habitat and others.
  • Ecotones - Boundaries between adjacent communities.
    • Sharp boundaries - Closed communities
    • Indistinct boundaries - Open communities
communities in transition
  • Ecological Succession
    • Primary Succession - A community begins to develop on a site previously unoccupied by living organisms.
      • Pioneer Species
    • Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site.
ecological succession
Ecological Succession
  • Ecological Development - Process of environmental modification (facilitation) by organisms.
  • Climax Community - Community that develops and seemingly resists further change.
    • Equilibrium Communities (Disclimax Communities) - Never reach stable climax because they are adapted to periodic disruption.
introduced species
Introduced Species
  • If introduced species prey upon or compete more successfully than native populations, the nature of the community may be altered.
    • Human history littered with examples of introducing exotic species to solve problems caused by previous introductions.
      • Mongoose and Rats in Caribbean
  • Critical Environmental Factors
  • Adaptation
  • Natural Selection
  • Speciation
  • Ecological Niche
  • Population Dynamics
  • Community Properties
  • Succession
  • Introduced Species