Transcript Ecology
Ecology Lecture 12 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 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 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 Note relationship between – Patch size and interior area – Patch shape and interior area Note different responses of birds to area 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 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 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 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 Ecosystem – Closed system No inputs – Open system At least one input – Three components Non-living Autotrophs Heterotrophs 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 Primary productivity varies with ecosystem Primary production varies with nutrient availability Primary production varies with time Primary productivity limits secondary productivity Secondary producers are not neceassarily highly efficient 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 Assimilation efficiencies vary widely among endotherms and ectotherms Pattern of flow varies Result is an ecological pyramid Describes loss at each level