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It discussed the adaptation of the vertebrates depending on the type of environment
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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• Predation – Trophic levels• Mutualism• Community Structure• Succession
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
Tolerance Limits
Limits of Range• Physical Barriers
Oceans (humans, cattle egrets, marsupials) Mountains (house finch) Ice (humans in the Americas)
• Climatic• Altitude• Food• Water• Competitors
Expanding Human Range
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
Adaptation is used in two ways:• Individual (moving from one
place to another)• Population (evolution)
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.
Speciation
• 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 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
Divergent evolution
Convergent evolution
Parallel Evolution
• two related species arise from a common ancestor. The two species then evolve in much the same way over time, probably in response to similar environmental selection pressures.
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.
Generalist species
Tree sparrows
Yellow vented bulbul
Specialist species
Philippine frogmouth
Philippine Eagle Silvery kingfisher
Competition
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.
Resource Partitioning
Predation
• 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
• 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 - 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 ( tigers, Phil. Eagle) Critical food organisms (bamboo and pandas)
( eucalyptus & koala) Often, many species are intricately
interconnected so that it is difficult to tell which is the essential component.
Competition
• 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
Mutualism
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
Commensalism: Epiphytes:
Symbiosis - Lichens
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 -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.
Productivity• 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)
• 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 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 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• 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
• 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 - 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
• 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
• 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.
Terrestrial Primary 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
• 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
Summary:
• Critical Environmental Factors• Adaptation• Natural Selection• Speciation• Ecological Niche• Population Dynamics• Community Properties• Succession• Introduced Species