John Latto 7/10/07 Ecology lecture 5 - Community structure I - population interactions A - Defining interactions by the effects on population density i) (+ -) A range of interactions defined by whether, and how many, prey are killed. Predation, Parasitism, Herbivory, Parasitoids Selective and unselective predators and their effects on the community. Keystone species Coevolution Population dynamics - a rich variety ii) (- -) Interspecific competition Interference competition vs. exploitation competition ‘Top-down’ vs. ‘bottom-up control of community structure Gause’s experiments Competitive exclusion principle and niche differentiation Classic experiment – barnacles in Scotland showing fundamental and realized niches Character displacement (allopatry and sympatry) Competition for ‘enemy free space’ ‘Ghost of competition past’ The ecological niche iii) (+ +) Mutualism Obligate vs. facultative, symbiotic vs. non-symbiotic A wide range of examples both familiar and unfamiliar: Those with reciprocal links in behavior; theose involving the culture of crops or livestock; pollination mutualisms; mutualisms involving gut inhabitatnts; thoseliving in insect tissues or cells; those involving higher plants and fungi; Mutualisms of algae with animals; mutualisms of fungi and algae; nitrogen fixation. iv) (+ o), (- o) Commensalism and amensalism B - Community structure i) Species diversity, species richness and relative abundance ii) Trophic interactions - food webs iii) Stability Ecology lecture 6 - Community structure II - disturbance, succession and food webs A - Succession i) Types of succession Primary succession vs. secondary succession Degradative succession Use of succession in forensic science ii) Mechanisms of succession: Facilitation, Tolerance, Inhibition iii) The influence of animals iv) The climax community v) Intermediate disturbance hypothesis vi) Practical applications: management of nature reserves; recovery from disturbance eg. fire; reclamation of land B - Food webs i) Types of food web Connectedness, Energy flow, Functional ii) Energy budgets Gross primary productivity vs. net primary productivity Primary and secondary productivity, Ecological efficiency, Pyramid of numbers iii) Patterns in food webs Length – generally short, 3 or 4 links from bottom to top. Why? Inefficient energy transfer limits them? Size or design constraints? Or, why are they so long? iv) Use of food webs: predicting pollutant movement and concentration; predicting community effects of introductions or extinctions; designing artificial communitiesJohn Latto 7/10/07 Ecology lecture 7 - Species diversity - patterns and maintenance A - Community classification: i) By structure ii) By dominant species iii) By dominant species at each level iv) By relative similarity v) By all the species B - Environmental Gradients Sharp boundaries or smooth gradations? Distinct ‘communities’ or more general variation? C - Patterns in biodiversity i) N-S gradients in diversity Some possible explanations: Longer time for evolution in tropics, faster evolution in tropics, greater structural complexity in the tropics, greater environmental stability in the tropics, ‘intermediate’ levels of disturbance in the tropics, higher primary productivity in the tropics. ii) Species-area curves – linear on a plot of Log Species vs Log Area On islands and on mainland areas Area vs. habitats D - Island Biogeography i) MacArthur & Wilson’s theory of island biogeography Balance between immigration rates and extinction rates Large vs. small islands, Near vs. far islands Predictions of the theory – a dynamic equilibrium with constant turnover Experimental tests of the theory – birds in a small wood and insects on mangrove islands Application of theory to reserve design (Single Large Or Several Small) Ecology lecture 8 - Biomes and biodiversiy A - Global change and biodiversity i) What is biodiversity? Genetic diversity, species diversity and ecosystem diversity i) Estimating species number and rates of species loss. What we don’t know: How many species there are. How many species are going extinct What we do know: The causes of particular extinctions and declines. B - Causes of species loss – many extinctions have multiple causes i) Habitat destruction and fragmentation Reduces absolute habitat, Increases the amount of ‘edge’ habitat, Increases the distance between habitat patches. ii) Hunting (for ‘fun’ and food). Short term economic gain encourages overexploitation. Tragedy of the commons ii) Introduction of alien species. Where they come from and why they are a problem. iv) Pollution and other causes C - Consequences of species loss - does it matter? i) Economic value (eg. food, medicines, materials) ii) Moral reasons (religious or ethical) iii) Ecosystem function (eg. nutrient cycling, pollination, soil production, CO2 uptake, O2 production) How much redundancy is there in ecosystems? Ecology lecture 9 - Ecology, environment and man A - Food production and pest control i) 6 billion and growing ii) Feeding everyone – more crop per land area or more land area for crops or keeping more of what we grow? iii) Pesticide problems iii) Biological control. Advantages: Highly selective, Cheap, Self propagating & self perpetuating, Resistance unlikely Can reach places pesticides can’t Disadvantages of biological control: Limits subsequent pesticide use, Can be slow to initiate, Does not eliminate pest, May attack non-target species B - Disease ecology i) Emerging and re-emerging infectious diseases ii) Ecology or Epidemiology i) Explanations for emerging diseases Changing human density and distribution, Changing human mobility and movement, Changing human behavior, Antibiotic resistance, Immunosuppression, Environmental Change. iv) Examples: Hantavirus, Lyme diseases and Bolivian Hemorrhagic
View Full Document
Unlocking...