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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
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


Introduction
Introduction

  • 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
SUCCESSION

  • 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

  • STILL NEED MORE PROCESS BASED APPROACHES



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



Biogeographical concepts

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


Biogeographical concepts
…cont

  • 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


Biogeographical concepts

Figure 9.7

Source: After Lack, 1971


Biogeographical concepts

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


Summary
Summary

  • 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