SCI11 MOD7

• Population community approach


  Ecosystems as a network of intersecting populations (structure and components)
• Abiotic environment


  Backdrop where biotic interactions occur
• Population community approach fails to see the bigger picture
• Process function approach


  • Ecosystems as pathways of matter and energy
  • Functions and processes are more important and more fundamental than the organisms performing them
• Process function approach misses out the importance of some species
• Hypothetical food web

  • Basal species
  • Intermediate species
  • Top predators
  • Keystone species
• Keystone species


  • Create or modify habitats and influence interactions among species
  • Impact is disproportionally large relative to its abundance
• Keystone species

  • Corals
  • African elephants
  • Wolves
• Ecosystem engineers

  Any organism that modifies a habitat
• Types of Ecosystem Engineers

  • Allogenic engineers (modify the environment by modifying materials from one form to another)
  • Autogenic engineers (modify the environment by modifying themselves)
• Allogenic engineers


  • Earthworms
  • Beavers
• Autogenic engineers


  • Corals
  • Trees
• Landscapes

  Heterogeneous area composed of several ecosystems
• Landscape matrix

  • The primary cover type in the landscape
  • Greater control over the flora and fauna
• Landscape patch

  Homogenous area that differs from the surrounding matrix
• Landscape corridor

  A strip of environment connecting 2 or more landscape patches of similar habitat
• Complexity theory

  Differs from other analytical approaches in that it is based upon a conceptual model in which entities exist in a hierarchy of interrelated organizational levels
• Parameters of a complex system

  • Numerosity - number of elements in different levels to the hierarchy within our system
  • Non linearity - interactions and feedbacks loop over time
  • Connectivity - indicate the degree of how things flow in the networks
  • Autonomy and adaptation - enables self organization and the process of evolution that shapes complex systems on macro scale (ecological memory)
• Dimensions of ecological complexity

  • Spatial
  • Temporal
  • Structural
• Spatial dimension


  • Distribution defines the spatial extent of a population/ ecosystem
  • Natural boundaries (edge, border, ecotone)
  • Edge effect - more variety of species at the borders or boundary of 2 or more habitats
• Temporal dimension


  • The time series of different variables describing the dynamics of a system
  • Changes in the population
  • Effects of changes in climate and weather
  • Extinction rate
  • Invasion rate
  • Succession
• Primary succession


  • Raw materials
  • Pioneer species
  • Intermediate
  • Climax community
  • Hundred years
• Secondary succession


  • Disturbance
  • Ecological memory
• Predator and prey cycles

  • Climax community
  • End of succession
• Structural dimension


  • Relationships within the ecosystem (food web)
  • Connectivity
• Types of networks


  • Planar
  • Random
  • Scale-free
  • Small-world
• Among the four kinds of networks, the more complex and ideal habitat may resemble a scale-free network with several large hubs connected to multiple smaller patches
• Hub


  A node with many connections
• Clustering and compartmentalization


  • Scale-free networks are highly resistant to random disturbances but vulnerable to deliberate attacks on the hubs
  • Clustering - disadvantage: facilitate the fast spread of disturbances, advantage: facilitate fast dispersal (i.e of seeds) that aids recovery to patch removal
  • Compartmentalization - disadvantage: connectivity would break apart if hubs were taken away, advantage: may isolate the potentially cascading effects of disturbance