ecology habitat vs niche

• Keystone species


  • Have significant and disproportionate effect on the community
  • Not only affects species that it has a direct relationship with, but also those other species that it no longer has direct contact with
  • Very strong cascading impacts on the structure and functioning of ecosystems
  • Its loss may lead to the collapse of the community
• Keystone species


  • Old World fruit bats as pollinators
  • Sea otter (Enhydra lutris) as a keystone predator feeding on herbivorous sea urchins
• Ecological niche


  • Biological role played by a species in the environment
  • Place or function of a given organism within its ecosystem
  • If no competition, organism occupies fundamental niche
  • With competition, organism occupies realized niche = conditions under which an organism actually lives
• Ecological Succession


  • Gradual changes of the vegetational community over time
  • Characterized by the replacement of early seral stage pioneer or opportunistic species by late-stage equilibrium species
  • In response to changes brought about by vegetation itself
• Stages of succession


  • Nudation - colonization of a disturbed area
  • Invasion - arrival of propagules/seeds of various organisms and their establishment in the new area
  • Competition and Reaction - replacement of more competitive, longer-lived species such as shrubs, and then trees
  • Stabilization and Climax - further changes take place very slowly, site is dominated by long-lived, highly competitive species
• Forms of disturbance

  • Large-scale disturbance - severe disturbance over a large area results in the colonization of the site by opportunistic species
  • Small-scale disturbance - small gaps typically result in reorganization of vegetation, important in maintaining diversity in tropical rainforest, results in patches of different stages of successional or compositional maturity, promotes species richness and structural diversity
• Climax stage of succession


  • An equilibrium or steady state with the environment
  • Last stage is mature, self-sustaining, self-reproducing through developmental stages, and relatively permanent
  • Vegetation is tolerant to changes in environmental conditions
• Theoretical approaches to climax

  • Monoclimax Theory - only one climax, determined solely by climate, with uniform plant and animal composition
  • Polyclimax Theory - mosaic of vegetational climaxes controlled by soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity
  • Climax Pattern Hypothesis - composition, species structure and balance of a climax community are determined by the total environment of the ecosystem