Biodiversity, Species Interactions, and Population Control

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Biodiversity, Species Interactions, and Population Control

  • Chapter 5

Where we’ve been…

  • Chapter 3
    • Looked at ecosystem components and how energy cycles within ecosystems
  • Chapter 4
    • Defined biodiversity. Looked at factors affecting biodiversity and how it is measured.

Where we are headed…

  • Chapter 5
    • Look at how species interact with each other and how ecosystems respond to changes in environmental conditions.

Species Interactions

  • Five Major Ways that Species Interact with one another:
    • 1. Interspecific Competition
    • 2. Predation
    • Symbiosis (two species living closely together)

Interspecific Competition

  • When two or more species interact to gain access to the same limited resources (food, water, light, space)
    • Intraspecific: same species competing for resources
    • Resource partitioning: species evolve traits to minimize competition with other species
    • As our footprint grows larger, we are impacting species even more (habitat loss)
      • Humans competing with other species for space and access to resources


  • When one member of a species feeds on a member of another species
    • Predator-prey relationship
    • Predators and prey often co-evolve traits that either allow them to find prey or hide from predators better
    • Predators play important roles in ecosystems (help to keep other species in balance)

Symbiotic Relationships--Parasitism

  • When one organism lives on or inside of another organism
    • Parasite benefits, host organism harmed (not immediately killed)
      • Parasite dies if host killed

Symbiotic Relationships--Mutualism

  • Interaction that benefits both species
    • Unintentional exploitation of the other organism (not cooperation)

Symbiotic Relationships-- Commensalism

  • Interaction that benefits one species and has little or no effect the other

Population Dynamics

  • Population: group of interbreeding individuals of the same species
    • Most organisms live together in clumps
  • Changes in population size influenced by:
    • Births and deaths
    • Immigration and emigration
    • Population change= (births + deaths) – (immigration + emigration)
    • Age structure diagrams can also be used to describe organism populations
    • -identify if population is growing, stable or declining

Limiting Factors

  • Populations have a range of tolerance. A set of physical and chemical conditions that they will thrive under.
    • Small variations in a population will exist due to genetic differences
    • “optimal range of tolerance”—conditions in which most organisms survive
    • Limiting factor principle: too much or too little of any physical or chemical factor can limit or prevent growth of a population
    • Examples of limiting factors?

Range of Tolerance

Carrying capacity: maximum number of individuals an ecosystem can support.

  • Carrying capacity: maximum number of individuals an ecosystem can support.
    • Environmental resistance: combination of all limiting factors determines carrying capacity
    • Exceeding carrying capacity causes population to crash
      • Overshoot and die off
  • Population density: number of individuals found in a particular area
    • Density dependent limiting factors
    • Density independent limiting factors
      • Weather events, fire, pollution, habitat destruction

Reproductive Strategies and Survivorship

  • R-strategist (type 1)
    • Many small offspring with little or no parental care
    • Large losses of young offspring, so produce large numbers to compensate
    • Examples: algae, bacteria, insects, some fish species
  • K-strategist (type 3)
    • Reproduce later in life, few offspring
    • Longer lifespan, mature slowly with parental care
    • Examples: mammals, birds
  • When graphed these two reproductive strategies produce unique survivorship curves
    • Classified as type 1, 2 or 3 depending on mortality rates

Type 1: low infant mortality and high survival

  • Type 1: low infant mortality and high survival
  • Type 2: constant decline
  • Type 3: high infant mortality few reach adult

Population Calculations

  • Annual Growth Rate
    • (CBR-CDR)/ 10 = % growth
      • ** Does not include immigration or emigration
  • Change in Population per year
    • Population change= (births + deaths) – (immigration + emigration)
  • Population Density
    • (Number of individuals) / (area sampled)
  • Doubling Time
    • 70/ annual growth rate = doubling time of a population
  • Birth and Death Rates
  • (births or deaths per year) / (Total Population)
  • **Crude birth and death rate multiply by 1000

Response to Ecosystem Change

  • Ecological Succession: gradual change in species composition in an ecosystem after a significant disruption
    • Primary succession: gradual establishment of living organisms in lifeless areas where there is no soil or sediment (aquatic)
      • bare rock, parking lots, new ponds or reservoirs, cooled lava
      • takes a very long time
    • Secondary succession: series of communities and ecosystems develop in places containing soil or sediment
      • abandoned farmland, burned/logged forests, polluted streams, flooded land
      • can relatively happen quickly

Succession increases species richness and complexity of food webs

  • Succession increases species richness and complexity of food webs
  • enhances energy flow and nutrient cycling which promotes increased biodiversity
  • does follow an unpredictable path
  • resilience of ecosystems: ability through succession to rebound to previous state after significant disturbance
    • rainforests highly complex and diverse, very difficult to return to previous state
      • “Ecological tipping point”—ecosystems won’t recover when past this point

Succession and Mt. St. Helens

  • May 18, 1980 erupted violently
  • Deadliest and most destructive volcanic eruption in US history
  • Eruption reduced the height of the mountain by 1300 feet

The Mt. St. Helens National Volcanic Monument was created to preserve the volcano as well as provide the land for scientific study.

  • The Mt. St. Helens National Volcanic Monument was created to preserve the volcano as well as provide the land for scientific study.

Article Reading and Questions

  • Read the article: Mt. St. Helens 30 Years Later
  • Answer the following questions.
    • Describe the impact of the MSH eruption on the surrounding ecosystem. Give specific details.
    • Describe how succession is reshaping the MSH ecosystem. What has been observed in the past 30+ years?
    • What are the concerns with the MSH ecosystem looking toward the future?

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