Evolution, Biological Communities, and Species Interactions

Outline Evolution and Speciation Species Interactions Community Properties Communities in Transition Introduced Species and Community Change

Definitions evolution - genetic changes within a population over time natural selection - differential reproductive success mutations - random changes in DNA adaptation - genetic trait that confers a selective advan- tage in a given environment

Critical Limits Von Liebig proposed the single factor in shortest supply relative to demand is the critical determinant in species distribution. Shelford later expanded by stating each environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive.

Tolerance Limits

Critical Limits For many species, the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution. For some organisms, there may be a specific critical factor that mostly determines abundance and distribution. Species requirements and tolerances can also be used as useful indicators. Environmental indicators

Variation Four conditions are necessary for evolution to occur 1. variation in traits in a population 2. traits must affect reproductive success 3. traits must be inheritable 4. some selective pressure must favor these traits differentially

Selective Pressure Environmental factors that favor survival and increase reproductive success of some individuals over others can lead to evolution. Natural selection modifies populations so that they are better suited to their environment.

resource partitioning - groups of individuals become specialized to utilize sub-sets of the same resource radiative evolution - divergence from common ancestor into two or more species

Reproductive Isolation Isolation prevents gene flow between members of a species Two types of speciation: allopatric - due to geographic separation sympatric - does not require geographic separation

Reproductive Isolating Mechanisms mechanical - structural differences temporal - different timing for breeding behavioral - courtship displays ecological - different ecological roles

Evolution at Work artificial selection pesticide and antibiotic resistance bioremediation

Evolution and Religion evolution as “God’s tool” “missing links” molecular support intelligent design punctuated equilibrium scientific theory

Ecological Niche Habitat - Place or set of environmental conditions where a particular organism lives. Ecological Niche - Description of the role a species plays in a biological community, or the total set of environmental factors that determines species distribution. Generalists - Broad niche Specialists - Narrow niche

Resource Partitioning Law of Competitive Exclusion - No two species will occupy the same niche and compete for exactly the same resources for an extended period of time. One will either migrate, become extinct, or partition the resource and utilize a sub-set of the same resource. Given resource can only be partitioned a finite number of times.

Resource Partitioning

SPECIES INTERACTIONS A predator is an organism that feeds directly upon another living organism, whether or not it kills the prey in doing so. Prey most successfully on slowest, weakest, least fit members of target population. Reduce competition, population overgrowth, and stimulate natural selection. Co-evolution

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. Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.

Competition Interspecific - Competition between members of different species. Intraspecific - Competition among members of the same species. Often intense due to same space and nutritional requirements. Territoriality - Organisms defend specific area containing resources, primarily against members of own species. Resource Allocation and Spacing

Symbiosis Symbiosis - Intimate living together of members of two or more species. 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 species evolve to look alike.

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 left after respiration.

Abundance and Diversity Abundance -Total number of organisms in a community. Diversity - Number of different species, ecological niches, or genetic variation. 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 ecological structure - patterns of spatial distribution of individuals and populations within a community random distribution clustered/clumped distribution - for protection, mutual assistance, reproduction, access to resources uniform distribution - often the result of competition Distribution can be vertical as well as horizontal.

Complexity and Connectedness Complexity - Number of species at each trophic level, and the number of trophic levels, in a community. Diverse community may not be complex if all species are clustered in a few trophic levels. Highly interconnected community may have many trophic levels, some of which can be compartmentalized.

Resilience and Stability Constancy (Lack of fluctuation) Inertia (Resistance to perturbation) Renewal (Ability to repair damage) MacArthur proposed complex, interconnected communities would be more stable and resilient in the face of disturbance. Controversial

Edges and Boundaries Edge Effects - Important aspect of community structure is the boundary between one habitat and others. Ecotones - Boundaries between adjacent communities. Sharp boundaries - Closed communities Indistinct boundaries - Open communities

Edges and Shapes

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.

Primary Succession

Ecological Succession Ecological Development - Process of environmental modification (facilitation) by organisms. Climax Community - Community that develops and seemingly resists further change. Equilibrium Communities (Disclimax Communities) - Never reach stable climax because they are adapted to periodic disruption.

Introduced Species and Community Change If introduced species prey upon or compete more successfully than native populations, 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

Summary Evolution and Speciation Species Interactions Community Properties Communities in Transition Introduced Species and Community Change