Transcript Lecture 6
Populations, Communities, and Species Interaction Chapter 3 Outline: • • • • • • • • Critical Factors and Tolerance Limits Adaptation and Natural Selection Speciation Ecological Niche Species Interaction Population Growth Community Properties and Structure Succession SPECIES INTERACTION • Predation - antagonistic Any organism that feeds directly on another living organism is termed a predator. Predation Influences: - All stages of predator and prey life cycles. - Specialized food-obtaining mechanisms. - Specific predator-prey adaptations. Predation can exert selective pressures. - Coevolution SPECIES INTERACTION • Competition - antagonistic Intraspecific - Competition among members of the same species. They cope by: - Dispersal - Territoriality - Resource Partitioning Interspecific - Competition between members of different species. Best suited will have advantage. SPECIES INTERACTION • Symbiosis - Intimate living together of members of two or more species (can be non-antagonistic). Commensalism - One member benefits while other is neither benefited nor harmed. - Cattle and Cattle Egrets Mutualism - Both members benefit. - Lichens (Fungus and cyanobacterium) Parasitism - One member benefits at the expense of other. Humans and Tapeworms Defensive Mechanisms Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species. Mullerian Mimicry - Two unpalatable or dangerous species evolve to look alike. Avoidance - camouflage Keystone Species • • Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance. eg, Top Predators or? Often, many species are intricately interconnected so that it is difficult to tell which is the essential component. Perhaps ‘keystone set’. Multiple Key Players Keystone species - species that play essential community roles & not just from abundance (examples: mycorrhizae, giant kelp) Community-level Interactions Keystone species??? (Botkin & Keller 2003) POPULATION DYNAMICS • Population Growth Exponential Growth – unrestricted growth. Growth as a percentage of the whole. - dN/dt=rN Biotic Potential - Potential of a population to grow in the absence of expansion limitations. Boom and Bust Cycles • Exponential growth is graphed as a J curve. • Carrying Capacity - Number of individuals that can be indefinitely supported in a given area. • Overshoot - When a population surpasses the carrying capacity of its environment. Dieback Oscillations Population Oscillations Population Oscillations Changes in pop: * No predators & lots of vegetation so moose increase, * Vegetation heavily eaten & decreases so moose crash, * Wolves arrive and moose decrease, * Wolves decrease w less genetic variation and canine virus introduced by dogs so moose increase…. * Moose decrease due to lack of food, poor reproduction, severe winter and tick infestation so crash…. Moose and wolves stabilize Abiotic & Biotic Controls Miller 2002 Isle Royal on Lake Superior Growth to a Stable Population • Logistic Growth - Growth slows as the population approaches carrying capacity. Limiting Factors • Environmental Resistance Density-Independent Factors - Effect on mortality rate is independent of population density. - Abiotic conditions. Density-Dependent Factors - Mortality rates increase as the density of the population increases. - Disease, Stress, Predation COMMUNITY PROPERTIES • Primary Productivity - Rate of biomass production. Used as an indication of the rate of solar energy conversion to chemical energy. Net Primary Productivity - Energy (amount of biomass) left after respiration. • • • • Abundance and Diversity Abundance -Total number of individuals of a species in an area. Diversity - Number of different species, or ecological niches, or genetic variation in an area. Abundance of a particular species often inversely related to community diversity. As general rule, diversity decreases and abundance within species increases when moving from the equator to the poles. Community Structure Random - individuals live wherever resources are available Ordered - often the result of biological competition Clustered - individuals of a species cluster together for protection, mutual assistance, reproduction, or to gain access to a particular environmental resource Edges and Boundaries • Ecotones - Boundaries between adjacent communities. Edge Effects - Important aspect of community structure is the boundary between one habitat and others. - May extend for 100s of meters - May produce differently-shaped habitat patches. Edges and Boundaries Ecotones- the boundaries between adjacent habitats • Often rich in species diversity Example: boundary between a forest and a meadow • Preserve Shape COMMUNITIES IN TRANSITION • Ecological Succession Primary Succession - A community begins to develop on a site previously unoccupied by living organisms. - Pioneer Species Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site. - Ecological Development Primary Succession – development of a community in an area previously unoccupied (vs disturbed community, then secondary succession) Mature forest Lichens (fungi+algae) Ecological Succession • • Climax Community - Community that develops and seemingly resists further change under a given climate. Clements – relay of plant species Individualistic Community - Species become established according to their ability to colonize and reproduce in a given area. Gleason Lodgepole Pine •Once thought of as ‘climax’ • Now considered ‘fire adapted’ Introduced Species • If introduced species prey upon, or compete more successfully than, native species, the nature of the community may be altered. Human history littered with examples of introducing exotic species to solve problems caused by previous introductions. - Mongoose and Rats in Caribbean Introduced Species and Community Change Key Points • • • • • Communities consist of an assemblage of populations (a population being a group of individuals of the same species that interbreed). Individuals with adaptations that improve their reproductive fitness are selected for. Natural selection works through inter- and intraspecific interactions (mutations & selective pressure). Populations oscillate before reaching equilibrium at the carrying capacity of the system. Communities often have repeatable structures and properties that exhibit parallel chronosequences following disturbances (primary and secondary succession).