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Chapter 5: Community Ecology. How do species interact?. Interspecific Competition. Members of two or more different species interact to gain access to the same limited resources Niches overlap; the greater the overlap, the more intense the competition

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interspecific competition
Interspecific Competition

Members of two or more different species interact to gain access to the same limited resources

  • Niches overlap; the greater the overlap, the more intense the competition
  • No two species can occupy the same niche for very long; Competitive Exclusion
  • Both species may suffer
intraspecific competition
Intraspecific Competition

Members of the same species interact to gain access to the same limited resources

  • Predator – prey relationship; 1 species feeds directly on all or part of another species; usually on live species
  • Help sustainability (ex. – kelp-urchin-otter)
  • Carnivores use either ambush or pursuit to capture prey
  • Ambush: camouflage is used; adapted by prey as well
  • Chemical warfare: used by spiders, snakes, to paralyze prey
  • Prey use adaptations such as speed, alert systems (senses) , avoidance (ex. – shells), mimicry and scare tactics
  • Role in natural selection: weeding out the weak, aged, sick in a population
  • Coevolution may occur; changes in one species gene pool leads to adaptive changes in another’s

One species (the parasite) feeds on the body of, or energy used by, another organism

  • Parasite is much smaller than host
  • May weaken but rarely kills host
  • Some live in host (tapeworms) some attach to outside of host (lampreys)
  • Some have little contact with hosts (cowbirds)
  • Coevolution can happen (malaria)

Interaction that benefits both species by providing food, shelter, or some resource

  • Pollinators
  • Birds that eat parasites off skin of other animals, also act as alarm system
  • Clownfish – anemone
  • Gut-inhabitant species

Interaction that benefits one species while other is not affected

  • Epiphytes such as orchids and bromeliads
resource partitioning
Resource Partitioning

When species competing for similar resources evolve traits that allow them to share resources at different times, ways, or places

  • Examples: warblers and honeycreepers

Populations differ in:

  • Distribution
  • Numbers
  • Density
  • Age structure

Population Dynamics studies changes in all the above in response to environmental changes

3 patterns of distribution
3 Patterns of Distribution
  • Clumping – example; desert vegetation around springs; location & size varies with availability of resources; offers advantages
  • Uniform Distribution
  • Random Distribution

Numbers vary cyclically

  • Population Change = (births + immigration) – (deaths + emigration)
  • Age Structure: proportions of individuals in various age groups
    • Pre-reproductive
    • Reproductive
    • Post-reproductive
indefinite population growth no
Indefinite Population Growth? No!
  • Biotic Potential: large animals at a disadvantage; low biotic potential
  • Intrinsic Rate of Increase (r): rate at which population would increase if unlimited resources are available
  • High r value: reproduce early, often, short generation time, produce many offspring
  • Scientific Principles of Sustainability – always limits population growth
environmental resistance
Environmental Resistance

Combination of all factors that limit population growth

  • With biotic potential, it determines the Carrying Capacity (k); the maximum population a habitat can sustain
  • Exponential growth: 1-2% increase; when graphed, produces a “J” curve
  • Logistic Growth: rapid exponential growth followed by a leveling off; when graphed, produces an “S” curve
population crash
Population Crash
  • No logistic curve is achieved
  • Brought on by a reproductive time lag in rates of births and deaths
  • Die-back occurs
  • Sometimes when a population exceeds k, it causes damages that reduce k (over-grazing in the US)
reproductive patterns
Reproductive Patterns
  • r-selected species: have many offspring, give little or no parental care, are opportunists, susceptible to population crash
  • K-selected species: reproduce later in life, produce small numbers of offspring, matire slowly, longer life spans, parental protection, logistic pattern
genetic diversity
Genetic Diversity

Affects smaller populations:

  • Founder Effect: a population colonizes a new habitat
  • Demographic Bottleneck: few individuals survive a catastrophe
  • Genetic Drift: random changes in gene frequency → unequal reproductive success
  • Inbreeding: increases frequency of defective genes
population density
Population Density

Number of individuals per unit area or volume

  • Density-Dependent Controls: predation, infectious disease, competition
  • High Density: successful reproduction, leads to increased competition
  • Abiotic Controls are density independent (ex. -
types of population change
Types of Population Change
  • Stable: population fluctuates slightly above and below its carrying capacity
  • Irruptive: occasional population explosion followed by a crash to stable level; algae, insects (summer – winter)
  • Cyclic: follow a top-down or bottom-up regulation
  • Irregular: no recurring pattern
humans not exempt
Humans not Exempt
  • Irish potato famine
  • Bubonic plague
primary succession
Primary Succession

A gradual establishment of biotic communities in lifeless areas where there is no soil in terrestrial ecosystems and no bottom sediment in an aquatic ecosystem

  • Examples: bare rock from glacial retreat, newly cooled lava, parking lot or highway, newly created pond or reservoir
  • Involves a pioneer species
primary succession1
Primary Succession
  • Slow process
  • Pioneer species begin soil formation (ex – lichens and mosses)
  • Followed by mid-successional plants (shrubs, grasses, herbs)
  • Late-successional plants (trees)
secondary succession
Secondary Succession

A series of communities or ecosystems with different species develop in places containing soil or bottom sediment

  • Occurs where an ecosystem has been disturbed, removed, or destroyed
  • Include abandoned farmland, burned or cut forests, heavily polluted streams, flooded land
secondary succession1
Secondary Succession
  • Both types of succession increase biodiversity and thus the sustainability of communities and ecosystems
  • Environmental disturbances can set both processes back
  • Succession does not follow a predictable path
stability in living systems
Stability in Living Systems
  • Inertia (Persistence): the ability of a living system to survive a moderate disturbance
  • Resilience: the ability of a living system to be restored through secondary succession after a moderate disturbance
  • Ecosystems are one or the other
  • Tipping point comes into play (systems dealing with multiple stresses)