CHAPTER 5

• Southern Sea Otter


  • Live in giant kelp forests on Pacific coast
  • Hunted almost to extinction by early 1900s
  • Partial recovery since listed as endangered in 1977
• Reasons to care about sea otters
• Five types of species interactions

  • Interspecific competition
  • Predation
  • Parasitism
  • Mutualism
  • Commensalism
• Interspecific competition


  Competition between different species to use the same limited resources
• Competitive exclusion principle


  Two species cannot occupy the same niche
• Resource partitioning


  Different species evolve specialized traits that allow them to share the same resources
• Predation


  • Predator feeds directly on all or part of a member of another species (prey)
  • Strong effect on population sizes and other factors in ecosystems
• Methods of predation


  • Herbivores walk, swim, or fly to plants
  • Carnivores use speed, flight, and senses to locate prey
  • Predators adapt camouflage and chemical warfare
  • Prey adapt protective shells, bark, spines, and thorns
• Prey species adaptations


  • Camouflage
  • Chemical warfare
  • Warning coloration
  • Mimicry
  • Behavioral strategies
• • Giant kelp anchored to ocean floor and grow toward surface
  • Fast growing
  • Resistant to storm and wave damage
  • Support many marine plants and animals
• Sea urchins prey on kelp plants

  Southern sea otter helps control sea urchin population
• Coevolution


  Changes in the gene pool of one species can cause changes in the gene pool of the other
• Coevolution example


  • Bats and moths
  • Echolocation of bats and sensitive hearing of moths
• Parasitism


  • One species (parasite) lives on another organism
  • Parasites harm but rarely kill the host
• Parasitism examples


  • Tapeworms
  • Sea lampreys
  • Fleas
  • Ticks
• Mutualism


  • Interaction that benefits both species
  • Nutrition and protective relationship
  • Not cooperation—mutual exploitation
• Mutualism example


  • Clownfish live within sea anemones
  • Gain protection and feed on waste matter left by anemones' meals
  • Clownfish protect anemones from some predators and parasites
• Commensalism


  Benefits one species and has little effect on the other
• Commensalism examples


  • Epiphytes (air plants) attach themselves to trees
  • Birds nest in trees
• Primary ecological succession


  • Involves gradual establishment of communities in lifeless areas
  • Need to build up fertile soil or aquatic sediments to support plant community
  • Pioneer species such as lichens or mosses
• Secondary ecological succession


  • Series of terrestrial communities or ecosystems develop in places with soil or sediment
  • Examples: abandoned farmland, burned or cut forests, and flooded land
• Factors affecting rate of secondary succession

  • Facilitation of area by one species for another
  • Inhibition hinders growth
  • Tolerance occurs when organisms are not in direct competition
• Traditional view of ecological succession

  • Proceeds to stable climax communities
  • Equilibrium called balance of nature
• Current view of ecological succession

  • Leads to a more complex, diverse, and resilient ecosystem
  • Can withstand changes if not too large or too sudden
• Ecological inertia or persistence

  Ability of a living system to survive moderate disturbances
• Resilience

  Ability of a living system to be restored through secondary succession after a moderate disturbance
• Population

  Group of interbreeding individuals of the same species
• Variables that govern changes in population size

  • Births
  • Deaths
  • Immigration
  • Emigration
• Age structure


  • Pre-reproductive stage
  • Reproductive stage
  • Post-reproductive stage
• Limiting factors

  • Precipitation (on land)
  • Water temperature, depth, clarity, and other factors (in aquatic environments)
  • Population density
  • Density-dependent factors
• 1. shaped growth curve


  • Some species can reproduce exponentially
  • Reproduce at an early age
  • Have many offspring each time they reproduce
  • Short intervals in between reproductive cycles
• Environmental resistance


  Sum of all factors that limit population growth
• Carrying capacity


  Maximum population of a given species that a particular habitat can sustain indefinitely
• 1. selected species

  • Species with capacity for a high rate of population growth
  • May go through irregular and unstable cycles in population sizes
  • Tend to be opportunists
• 1. selected species


  • Species that reproduce later in life
  • Have few offspring
  • Have long life spans
  • Can be vulnerable to extinction
• • 1900: deer habitat destruction and uncontrolled hunting
  • 1920s–1930s: laws to protect deer
  • Current deer population explosion in suburban areas
  • Increased deer-vehicle collisions and Lyme disease
• • Factors in declining sea otter population
  • Increased predation by orcas
  • Toxic algae and pollutants released into the ocean
  • Low reproductive rate
  • Rising mortality rate
  • Other threats: oil spills and fishing traps
  • Otter population rising in last several years
• Survivorship curve

  • Shows the percentages of members of population surviving at different ages
  • Late loss (K-selected species)
  • Early loss (r-selected species)
  • Constant loss (many songbirds)
• Mature white oak (Quercus alba) produces thousands of acorns per year, which serve as an important food source for many animals. Mature trees have an average lifespan of 300 years.
• Technological, social, and cultural changes have expanded earth's carrying capacity for the human species today