Biological Communities and Species Interaction

1
Biological Communities and Species Interaction
2
Important Concepts

• Critical Environmental Factors
• Adaptation
• Natural Selection
• Speciation
• Ecological Niche
• Population Dynamics
• Community Properties
• Succession
• Introduced Species

3
Types of Species Interactions

• Competition
• Predation Trophic levels
• Mutualism
• Community Structure
• Succession

4
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

5
Tolerance Limits
6
Limits of Range

• Physical Barriers
• Oceans (humans, cattle egrets, marsupials)
• Mountains (house finch)
• Ice (humans in the Americas)
• Climatic
• Altitude
• Food
• Water
• Competitors

7
Expanding Human Range
8
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

9
Adaptation

• Adaptation is used in two ways
• Individual (moving from Alabama to Wisconsin)
• Population (evolution)

10
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.

11
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.

12
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

13
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.

14
Competition
15
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.

16
Resource Partitioning
17
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)

18
Co-Evolution and Disease

• If a disease kills too quickly, it cant 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)

19
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.

20
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

21
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

22
Commensalism Epiphytes
23
Symbiosis - Lichens
24
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.

25
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.

26
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

27
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

28
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

29
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

30
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

31
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)

32
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.

33
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

34
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

35
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.

36
Terrestrial Primary Succession
37
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.

38
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

39
Summary

• Critical Environmental Factors
• Adaptation
• Natural Selection
• Speciation
• Ecological Niche
• Population Dynamics
• Community Properties
• Succession
• Introduced Species