Ecology

1. Ecology Lecture 12

2. Landscape Ecology • Ecological system aare made up of mosaics of patches containing different ecologies • Landscape ecology studies how these patches form and continue to exist • A patch is a relatively homogenous area that differs from its surrounding area • Patches vary in size • Many patches make up the matrix • Patches form both naturally and due to human intervention • Human intervention is usually dominant in many area • Other forces are geology, fire, grazing • Size of patches can vary from meters to kilometers • When patches meet, they interact • These are called transition zones

3. Most obvious feature of a transition zone • Edge of each patch • Change in physical conditions • When long term physical features fit edge • Inherent edge • Stable • Edges due to natural disturbance, e.g. fire, or human intervention • Induced edge • Less stable and may require continuous maintenance • Place where one edge meets another edge • Border • Two edges and a border • Boundary • Can be sharp • Can be gradual, namely an ecotone • Boundaries can be very different to either patch • Edge effect • Certain species of animals and plants prefer boundaries and ecotones. Some species only inhabit edges • Edge species • Plants • Shade intolerant • Better tolerant of dry conditions • Animals • Require two plant communities to survive and reproduce

4. Mosaic of patches, edges and boundaries is not stable • Human continuous fragment patches • If size of patch becomes to small • Local extinction occurs • What size of patch maintains greatest diversity of species • At what size due area-sensitive species disappear • Large patches • Greater population density • Greater species richness • Support more individuals in their optimal environment • Large carnivores require a large home range and are therefore limited by small patches • Only when a patch is large enough will the edges be far enough away for the development of proper interior conditions • Interior species • Need stable environment • Area sensitive • Some species are area insensitive

5. Note relationship between • Patch size and interior area • Patch shape and interior area • Note different responses of birds to area

6. Island biogeography works for patches • Large island have more species than small islands • Equilibrium is reached when immigation equals extinction rate • However, species still change • Turnover rate • Larger island have a lower extinction rate • More variety of habitats • Any patch separated from other similar patches by inhospitable terrain can be treated as an island • Note effects of size and distance to nearest similar environment • Note also that there are fewer barrier to movement in a fragmented landscape than for a oceanic island • Corridors exist on land • Join patches • Hedgerows, ditches, bridges

7. Patches form metapopulations • Metapopulations decrease vunerability to local extinction • See movement by corridors and immigration • Patches • Inbreeding • Increase in homozygosity due to mating with close relatives • Genetic drift • Change in gene frequency due to sampling effect of small population causing allele loss • Minimum viable population • Effective size >100 • Actual size >1000 • Metapopulation >? • Sources patches • Reproductive rate exceeds mortality • Sink patches • Reproductive rate less than mortality

8. Disturbances affect communities • Fire, flood, drought, etc • Single event • Rare • Regular event • Linked disturbance regime • Intensity • Proportion of total biomass killed • Scale • Spatial extent • Frequency • Events per unit time • Small scale • Loss of a single tree • Creates gap • New conditions for colonization • Reorganization of populations close to site • Large scale • Intensity and scale are large • Local extinction • Change to sites physical environment

9. Examples of disturbance effects • Fire • Some seeds need fire to germinate • Surface fire • Burns litter only • No harm to roots, stalks, tubers, etc • Crown fire • Burns tops of plants, kills patches down to ground allowing migration • Ground fire • Cosumes all organic matter down to bare rock or minerals • Irreversibly changes landscape • Herbivores • Seed distribution • Elephant in game parks • Man • Forests • Madagascar and tropical rain forest cover

10. Ecosystem • Closed system • No inputs • Open system • At least one input • Three components • Non-living • Autotrophs • Heterotrophs

11. Input • Fixation and transfer of energy from Sun • Increase in net primary production by autotrophs • Goes into different sectors of biomass • Affected by • Rainfall • Temperature • Length of photosynthetic period • Evapotranspiration

12. Primary productivity varies with ecosystem

13. Primary production varies with nutrient availability • Primary production varies with time

14. Primary productivity limits secondary productivity • Secondary producers are not neceassarily highly efficient

16. Normally ecosystems have two major food chains • Terrestial grazing chain not very important • Only 2.6% of primary production • Insects very important • Detrital chain is very important • 35% of primary production • Food chains are interconnected • Energy flows through trophic levels • Energy decreases with each tropgic level

17. Assimilation efficiencies vary widely among endotherms and ectotherms • Pattern of flow varies

19. Result is an ecological pyramid • Describes loss at each level