BIOGEOGRAPHICAL CONCEPTS

1. 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

2. 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

3. 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

4. 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

5. Table 9.1

6. 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

7. Figure 9.4

8. Table 9.2 Source:From Spellerberg et al., 1999

9. 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

10. 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

11. 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

12. Figure 9.5

13. Figure 9.6

14. 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

15. …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

16. Figure 9.7 Source: After Lack, 1971

17. Figure 9.8 Source: After Yalden, 1999

18. 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)

19. Figure 9.9

20. 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

21. 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

22. 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