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BIOGEOGRAPHICAL CONCEPTS. Learning objectives: Understand key concepts within biogeography Understand processes causing changes in biogeographical distributions over time and space Describe the basic principles of landscape ecology Understand the theory of island biogeography

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biogeographical concepts
  • Learning objectives:
    • Understand key concepts within biogeography
    • Understand processes causing changes in biogeographical distributions over time and space
    • Describe the basic principles of landscape ecology
    • Understand the theory of island biogeography
    • Show awareness of current issues in biogeography
  • Biogeography is the study of the spatial distribution of plants and animals
  • Biogeography is an important area of science – it informs environmental policy and local land management
  • Biogeography recognises that to understand and manage current patterns requires examination of the processes that created these distributions
  • Very strong links with ecology
  • Very important concepts
    • succession, strategies used by plants and animals and the effects of habitat disturbance
  • Common themes
    • role of time, geological history and ecological processes
  • Succession = directional change usually leading to increased complexity of community structure and increased biodiversity
    • Primary succession
    • Secondary succession
  • When studying succession we substitute space for time
development of succession theory
Development of succession theory
  • Clements (1916>)
    • Observed a series of communities replacing each other
    • Climax community
    • Nudation, migration, ecesis, competition, reaction, stabilisation
  • Tansley – noted that environmental influences control climax type
  • Gleason (1926) – opposite
    • Assumed communities exist by chance resulting from their individual response to the environment
    • There is no true directional succession – frequent disturbances
  • Whittaker (1953>)
    • Climax communities reflect environmental gradients - ecocline
    • Within this is a central community type
    • Self maintaining climax pattern model
spatial patterns and process global scale
Spatial patterns and process: global scale
  • Climate
    • Patterns of species distribution heavily influenced by light and moisture availability
    • Climate closely interacts with the other factors
  • Geological factors
    • Tectonic movement create barriers to species dispersal
    • Wallace’s Line
  • Ecological factors
    • Habitat conditions (competition, space, predators/prey, migration abilities)
    • Speciation processes – Darwinist evolution of new species
      • Primary endemism and secondary endemism
      • Disjunct – wide gaps between species
    • Vital attributes will determine groups of species
      • Mobility of species varies greatly

Table 9.2

Source:From Spellerberg et al., 1999

spatial patterns and process small scale patterns
Spatial patterns and process: small scale patterns
  • Smaller-scale nested patterns relate to:
    • Availability of light, water, nutrients, intensity of human disturbance etc
  • ‘Disturbance gradient’ caused by humans
spatial patterns and process landscape ecology
Spatial patterns and process: Landscape ecology
  • 1939 Troll
    • “Study of the entire complex cause-effect network between the living communities and their environmental conditions which prevail in a specific section of the landscape…and becomes apparent in a specific landscape pattern”
  • Major growth area in biogeography, land planning, conservation
    • Identifying species habitats and functions
    • Measuring through landscape stability how likely it is a pattern may change over time
  • International Association for Landscape Ecology identify 4 themes
    • Spatial pattern/structure of the landscape (wilderness to cities)
    • Relationships between pattern and process in landscapes
    • Relationship of human activity to landscape pattern, process and change
    • Effect of scale and disturbance on the landscape
landscape ecology continued
Landscape ecology continued
  • Landscape patches
    • Distinctive elements within the landscape e.g. pond, wood or town
    • Patch characteristics, frequency, origin and stability indicates vulnerability and influence of other factors
      • e.g. shape indicates susceptibility to ‘edge effects’
    • Origin of patch determines other characteristics- new/old
      • E.g. polders, change in environmental conditions
  • Landscape matrices
    • Element that occupies a greater area than any patch type within it
    • Contains patches and corridors – control the character of the place
    • May be >1 matrix dominating e.g. savanna-forest boundary
  • Landscape corridors
    • Narrow strips that differ from the matrix on either side attached to a patch
    • Connectivity with similar corridors and other landscape features
    • Can increase mobility of wildlife e.g. hedgerows o decrease it e.g. pylons
temporal patterns and distributions
Temporal patterns and distributions
  • Geological time
    • Large scale mass extinctions (5 in the last 600 million years)
    • Dinosaur extinctions – 65 million yrs ago
    • Many causes proposed – asteroid impact, rising sea levels, extended environmental changes e.g. climate
  • Postglacial change
    • Quaternary climatic change (last 2 million yrs)
    • Many changes were slow enough for response
    • Areas such as Southern Europe became refuges for more northern species during cold periods
      • The British Isles are relatively species poor for their latitude because post glacial sea level rise meant dispersal mechanisms were inefficient over water bodies
  • Migratory patterns
    • Causes biogeographical change over time in a recurring pattern over a long period
    • Summer and winter distributions may be very distant from each other and also very different scales
  • Alien introductions
    • A species not part of the ‘native’ biogeography
    • Colonisation can be very rapid – far out-competing local species
    • Species poor islands are susceptible to invasions
      • Environmental niches not entirely filled
      • Parasites/predators/diseases absent or utilise other species
      • Certain habitat management techniques favour alien species
      • Human colonisers deliberately brought new species e.g. Grey squirrel in UK

Figure 9.7

Source: After Lack, 1971


Figure 9.8

Source: After Yalden, 1999

biogeographical modelling island biogeography
Biogeographical modelling: Island Biogeography
  • Islands can act as scientific laboratories
    • Biogeography is simplified due to a lack of external factors
  • MacArthur and Wilson (1967) suggested a relationship between the species richness on an island and its size and isolation
    • Rate of immigration
    • Biological diversity
    • Rate of extinction
  • New oceanic islands versus new ‘continental’ islands
  • ‘Virtual’ islands – landscape patches
    • Extensive applications for conservation strategies
      • Single large patch - Wilson (1994) and Diamond (1975)
      • Or several smaller patches - Simberloff (1983) and Maarel (1997)
biogeographical modelling species distribution modelling
Biogeographical modelling: species distribution modelling
  • Economic interest in biogeography
    • Increase efficiency of production
    • Control pests
    • Impact of climate change on pest distributions
  • Species have a preferred ecological niche and less favourable wider area they can survive
  • Can directly measure the species populations and related to conditions
  • Movement of a species can then be predicted e.g. with changing climatic conditions
  • E.g. the Ecoclimatic Index shows changing distribution of the fruit fly
biogeography and environmental change
Biogeography and Environmental Change
  • Need for land makes multiple land-use demands common
  • Management of wild and semi-wild plants and animals may have a variety of objectives, methods and levels of intensity
  • Important management aspects
    • Agriculture – ‘directed’ succession
    • Conservation – increase biodiversity
    • Recreation
    • Environmental tools – e.g. grasses for slope stability
  • May involve land reclamation or restoration
    • Need knowledge on species interaction with environment
    • Some areas with harsh conditions may enable specific species
      • e.g. areas with high levels of heavy metals in the soil allow new distinctive plant associations to develop that otherwise would not
  • Important factors
    • Large scale factors – climate and tectonics
    • Ecological factors – succession, evolution, extinction, species mobility, alien immigration
    • Smaller scale – topography, pedology
  • Landscape ecology – useful concept for exploring regional distributions
    • Matrix, patches, corridors
  • Underlining theme = change in the distribution of living things
    • Habitats develop and change in response to gradual or dramatic changes – community response
  • Island biogeography theory
    • Equilibrium point for the number of species an area can sustain
    • Criticisms but also practical applications
  • Biogeography has a wide range of applications in environmental management