EcosystemsStructure and DynamicsCommunity Ecology The scientific study of interactions among organisms and between organisms and their environments.
Ecosystems: Everything Is ConnectedEverything in an ecosystem is connected.What affects one part of an ecosystem often affects many other parts of the ecosystem as well.
Organisms and SpeciesAn organism is a single living thing.
A species is a group of organisms that can produce fertile offspring with the same characteristics.
PopulationsA population is a group of organisms from the same species living in the same place.There may be thousands of populations for any particular species.
A group of populations of different species living close enough to interact Interspecific interactions = all the species in a given area.
Some habitatsForestTreeLake or pondCity parkCaveFen or swamp or marshlandReef
HabitatAny place within the ecosystem where a population or community lives
SpeciesPopulationCommunityEcosystemBiomeBiosphereLevels of OrganizationBiome
Interaction in Communities
Community interactions are classified by whether they help, harm, or have no effect on the species involved.Co-evolution is a result of this history of interaction
When two species use the same resource, they participate in a biological interaction called competitionCompetition Shapes Communities
How Competition Shapes Communities Intraspecific between individuals of the SAME speciesInterspecific between individuals of DIFFERENT species
How Species Interact With Each OtherEcosystems work best when every niche in it is filled.Species interact with each other in many ways. The most common relationships are:PredationCompetitionParasitismMutualismCommensalism
Central to Competition and CommunityHabitat & microhabitat (Space utilization)Food spectrum, essential nutrients Reproductive requirementsNutrition, nest/den sitesSeasonality: When are resources required, usedOften described in terms of how the organism affects energy flow within the ecosystem, it is a pattern of livingTo understand how competition influences the makeup of communities, you must look at the functional role of the speciesThe Ecological Niche
PredationIn predation, one organism eats another.The animal that kills and eats is the predator.The animal that is eaten is the prey.Predators typically kill the young and weak/sick members of their prey. Consequently they help limit the size of the prey population.As the prey die off, the predators either switch their prey or die off also.This creates a specific cyclical relationship between predators and prey.
PredationHare cycles may be caused by increasing food shortages during winter caused by overgrazing Or they may be due to predator-prey interactionsCycles could be affected by a combination of food resource limitation and excessive predationPredators reproduce more slowly than their prey so they always lag behind prey in population growth.
Herbivory +/- interaction in which an herbivore eats part of a plant.It is advantageous for an animal to be able to distinguish toxic from nontoxic plants.A plants main protective devices are chemical toxins, spines, and thorns.
Interaction By Symbiosis
Two organisms living together in close association.
A symbiotic relationship in which both species benefit +/+Mutualism
Parasitism is a relationship between two organisms in which one feeds off another. The organism that feeds off the other is the parasite.The organism that contains the parasite is the host.The main difference between parasitism and predation is that in parasitism, the parasite does not usually kill the host quickly.
Commensalism One member benefits while other is neither benefited nor harmedmites hitching a ride on a beetle
Population Niche Fundamental niche The entire range of opportunityThe organisms potential (the role it could play) in the absence of biotic enemies depends on physical (abiotic) conditions. Realized nicheThe actual range of the organism (the role it does play in the community) in the presence of biotic enemies depends on biotic as well as abiotic conditions
Competition and Limitation of ResourcesBarnacles compete for space on rocky intertidal shores What is the realized niche of each barnacle?What is the fundamental niche of each?
Competition and Limitation of Resources
growthrateLocation in intertidal zonelowhighmiddleChthamalus aloneBalanus aloneHow can we determine the fundamental niche of each barnacle?Removal experiments remove each species and see where the other growsBalanusfundamental nicheChthamalus fundamental niche
growthrateLocation in intertidal zonelowhighmiddleHow can we determine the realized niche of each barnacle?Where do they grow when allowed to compete?Balanusrealized nicheChthamalus realized nicheBalanus
ChthamalusCompetition and Limitation of Resources
Two species cannot coexist if they occupy the same niche)
Law of Competitive ExclusionNo two species can occupy the same niche and compete for exactly the same resources for an extended period of time.One will either migrate, become extinct, or the two species will partition the resource and utilize a sub-set of the same resource.Given resource can only be partitioned a finite number of times.
Avoiding CompetitionResource partitioning sympatric species consume slightly different foods or use other resources in slightly different waysCharacter displacement sympatric species tend to diverge in those characteristics that overlap Ex: Anolis lizard sp. perching sites in the Dominican Republic Ex: Darwins finch beak size on the Galapagos Islands
Measures the number of different species in the community (species richness) and the relative abundance of each species.Community with even species abundance is more diverse than one in which one or two species are abundant and the remainder are rare.
Keystone SpeciesExerts strong control on the community structureThe affect on its community or ecosystem is much larger and more influential than would be expected from mere abundance.Often large predatorsCritical food organisms (bamboo and pandas)Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.Picky predators can promote coexistence among competing prey species.Competitive exclusion is prevented when the dominant competitor is the preferred prey.
Barnacles MusselsBalanus MytilusStarfishPisasterStarfish are picky they prefer to eat mussels (dominant competitor), allowing barnacles (weaker competitor) to coexist.How do starfish promote coexistence?How Keystone Species Affect Community Structurepreditorcompetitors