Communities and Ecosystems

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Chapter 19

• Communities and Ecosystems

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Communities

• Assemblies of populations in the same area that
  can potentially interact
• All the plants, animals and other organisms

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4 Levels of a Community

• Diversity
• Prevalent forms of vegetation
• Stability
• Trophic Structure

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1. Diversity

• Variety of different kinds of organisms in the
  community
• 2 components
• species richness total number of different
  species in community
• relative abundance of different species
• Both components are group together by ecologists
  as species diversity key to the maintain the
  health of the ecosystem

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Diversity

• May miss a species of trees in Community 2
  because of the predominance of 1 species
• Same number of species in each but most would say
  that Community 1 is more diverse because of even
  distribution of species

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2. Prevalent Form of Vegetation

• Mainly pertains to terrestrial communities
• See dominant plant but must also look at plant
  arrangement or structure
• structure is whether it is in the canopy,
  subcanopy or below the subcanopy
• Types of plants and structural features will
  determine the animals in the community

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3. Stability

• Communities ability to resist change and return
  to original species composition after a
  disruption
• depends on type of community and type of
  disruption
• cedar/hemlock forest is stable (thousands of
  years old) and can withstand isolated lightening
  strike fire with small shrubs/trees being damaged
  but a big fire can cause damage and it will take
  longer to recover
• may seem less stable in trying to re-establish
  itself

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4. Trophic Structure

• Feeding relationships among various species
• determines passage of energy and nutrients from
  photosynthetic organisms to herbivores to
  carnivores

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Interspecific Interactions in Communities

• Interactions between species
• 3 types of interations
• competition between species
• predation
• symbiosis

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Competition

• Occurs when species need to use similar limiting
  resources
• Population growth of species may be limited by
  density of competing species may be food,
  shelter, nesting sites or other resources

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Competition for Food

• 2 species of paramecium can grow to carrying
  capacity when grown individually, but in the same
  environment one strain becomes extinct
• other paramecium had a competitive edge over the
  other and reproduced more rapidly
• called competitive exclusion principle

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Niche

• Niche is sum total of a species use of biotic and
  abiotic resources in its environment organisms
  ecological role
• fit into the ecosystem
• Reword the competitive exclusion principle to
  state 2 species cannot coexist in ecosystem if
  niche is identical, only coexist if one or more
  differences in niche

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Resource Partitioning

• Differentiation of niches that allows similar
  species to coexist
• 2 outcomes to organisms sharing identical niches
• Less competitive will become locally extinct or 1
  species adapts to use a different set of resources

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Predation

• Organism (predator) eating other organisms (prey)
• Herbivory animals eating plants even is plant
  isnt killed
• Predation is important factor in evolutionary
  adaptation eating and not being and not being
  eaten leads to reproduction success
• natural selection refines the adaptations

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Predator Adaptation

• Acute sense of smell, claws, teeth, fangs,
  stingers or poisons to help subdue prey
• Herbivorous insects get right food using chemical
  sensors on feet
• Plant defense against herbivores use chemical
  toxins along with spines or thorns to protect
  against being eaten
• many of these compounds can be used by humans
  nicotine, morphine, etc spices, produce insect
  hormones that prevent insect development

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Animal Defenses

• Use passive defenses such as fleeing to shelter
  which uses lots of energy
• Large animals may use active defense to defend
  their young

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Additional Mechanisms

• Mob the predator with several members of
  community
• Distract away from nest by pretending to be
  injured, move further away from nest

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More Mechanisms

• Cryptic coloring to camouflage blends into
  environment
• Mechanical or chemical defenses
• toxins that collect from plants they eat or
  synthesize themselves
• warning color predators recognize color as
  something bad
• skunks spray and porcupine needles

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Mimicry as Defense Mechanism

• Batesian mimicry non-harmful mimics harmful
• moth puffs up to look like a venomous snake and
  even hisses
• Mullerian mimicry 2 or more unpalatable species
  mimic each other predator will ignore both
• Predators also use mimicry
• snapping turtle has a tongue that acts like a
  worm to attract a fish

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Predation and Species Diversity

• Predator-prey relationship helps to preserve
  diversity
• Remove major predator and actually saw a decrease
  in the other species rather than an increase
• Keystone predator species reduces density of
  strongest competitors in a community
• prevents competitive exclusion of weaker
  competitors
• Predation can be constructive

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Symbiotic Relationship

• Interaction between 2 or more species that live
  together in direct contact
• Parasitism is one type one organism benefits
  and the other is harmed
• parasite usually is small and gets nutrients by
  living on or in the host
• specialized type of predation
• Parsite usually has a specific host and it is a
  stable relationship and host is not killed
  immediately that would be bad for parasite

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Mutualism as Symbiotic

• Mutualism benefits both parties
• Acacia trees and ants live together
• ant eats the herbivorous insects and competing
  plants
• tree provides sugar and proteins in special
  glands for the ants, also live in the tree
• Flowering plants provide nectar and pollen to
  pollinators that then move some pollen to the
  next plant they visit

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Complexity in Community Networks

• Branching of the previous interactions is very
  complicated especially as communities change
• Some plants put out chemical attractants to bring
  in parasitic wasps that lay eggs in the
  caterpillars that eat the plant, both wasp and
  caterpillars are prey for spiders and birds which
  can be hosts for specific parasites

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Disturbances of Communities

• Damage to biological communities at least
  temporary
• destroys organisms and alter availability of
  resources
• storms, fires, floods, severe erosion, draughts,
  and human activities like deforestation and
  grazing
• disturbances usually happen one on top of the
  other

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Ecological Succession

• Communities change after a disturbance variety
  of species colonize disturbed area and then
  eventually replaced
• Primary succession community arises from a
  lifeless area with no soil
• Secondary succession disturbance occurs but
  leaves the soil intact
• usually recolonize with herbaceous (non-woody)
  plants that grown from wind blown or animal borne
  seeds, eventually replaced with woody shrubs

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Primary Succession
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Dynamic View of Community Structure

• Disturbances keep community in continual flux
  patches of successional stages
• no state of equilibrium or complete balance
• create new opportunities for species to enter
  community

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Ecosystem Dynamics

• Ecosystem all organisms in a given area plus
  physical environment soil, water, air
• 2 major processes
• energy flow passage of energy thru components
  of ecosystem
• light thru plants and lost as heat
• chemical cycling use/reuse of chemical elements
  such as C and N within the ecosystem
• recycle thru trophic structure main source of
  nutrition

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Tropic Levels and Food Chains

• Food chain is transfer from trophic level to
  tropic level
• Move from producers (autotrophic) which support
  all the other levels
• Humans are carnivores in the secondary consumer
  level
• KNOW the 5 levels

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Detritivores

• Most food chains do not include the detritivores
  that break down wastes and dead material
• Most common are prokaryotes and fungi as well as
  earthworms, rodents, insects, vultures, crayfish

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Food Web

• Combinations of food chains
• Omnivores eat consumers as well as producers