Transcript Understanding Our Environment

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
Alabama to Wisconsin)
• 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
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.
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
 Critical food organisms (bamboo and pandas)
 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