Ecology Biological Communities NO species exists independently of other species

The Community A group of populations of different species living close enough to interact Interspecific interactions between populations of different species within a community

Community structure Community~ an assemblage of populations living close enough together for potential interaction Richness abundance and distribution of numbers of different species Species diversity number of different species Hypotheses: Individualistic chance assemblage with similar abiotic requirement Interactive~ assemblage locked into association by mandatory biotic interactions

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

How Competition Shapes Communities When two species use the same resource, they participate in a biological interaction called competition

How Competition Shapes Communities Intraspecific – between individuals of the SAME species Interspecific – between individuals of DIFFERENT species

Interspecific Competition Competition occurs when resources are in short supply Competition is -/- interaction between the species involved

Competition evidence Resource partitioning~ sympatric species consume slightly different foods or use other resources in slightly different ways Character displacement~ sympatric species tend to diverge in those characteristics that overlap Ex: Anolis lizard sp. perching sites in the Dominican Republic Ex: Darwin’s finch beak size on the Galapagos Islands

Central to Competition and Community 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. The Ecological Niche

Interaction By Predation The act of one organism killing another for food +/- interaction Often involves keystone species

Types of predators Carnivores – kill the prey during attack Herbivores – remove parts of many prey, rarely lethal. Parasites – consume parts of one or few prey, rarely lethal. Parasitoids – kill one prey during prolonged attack.

Cryptic Coloration Striking adaptations often characterize predators and their prey Predators may evolve cryptic morphology (camouflage)

Cryptic Coloration Prey may evolve to blend in too! Camouflage

Prey may evolve warning morphology Aposematism Prey may evolve warning morphology Aposematic colors = warning

Mimicry Batesian mimicry Organisms may evolve to look like other organisms Batesian mimicry harmless mimic evolves to look like harmful model looks like something that is dangerous or tastes bad Viceroy Monarch Milk Snake Coral Snake

Mimicry Mullarian mimicry Two bad tasting organisms resemble each other, ostensibly so that predators will learn to avoid them equally. Mullarian mimicry Bracoria Millipedess Nudibranchs

Predation defense review Cryptic (camouflage) coloration Aposematic (warning) coloration Mimicry~ superficial resemblance to another species √ Batesian~ palatable/ harmless species mimics an unpalatable/ harmful model √ Mullerian~ 2 or more unpalatable, aposematically colored species resemble each other

Interaction By Symbiosis Where two organisms live together in close association. Can be mutually beneficial or benefit one organism and leave the other unharmed

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 plant’s main protective devices are chemical toxins, spines, and thorns.

Commensalism One member benefits while other is neither benefited nor harmed mites hitching a ride on a beetle

A symbiotic relationship in which both species benefit +/+ Mutualism A symbiotic relationship in which both species benefit +/+

Parasitism Parasites derive nourishment from their hosts +/- interaction endoparasites ectoparasites Tapeworm Tick

Ecological Niche Niche Often described in terms of how the organism affects energy flow within the ecosystem, it is a pattern of living To understand how competition influences the makeup of communities, you must look at the functional role of the species: Niche Habitat & microhabitat (Space utilization) Food “spectrum,” essential nutrients Reproductive requirements Nutrition, nest/den sites Seasonality: When are resources required, used. NOT TO BE CONFUSED WITH: Habitat - location where a particular organism lives

What is the niche? set of conditions multi-dimensional with as many within which an organism can maintain a viable population multi-dimensional with as many dimensions as their are limiting conditions ecological niche light intensity okay temperature salinity

Size of the Niche Fundamental niche Realized niche The entire range of opportunity The organism’s potential (the role it could play) in the absence of biotic enemies depends on physical (abiotic) conditions. Realized niche The 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 Resources Barnacles 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 How can we determine the fundamental niche of each barnacle? Removal experiments – remove each species and see where the other grows Balanus alone Balanus fundamental niche growth rate Chthamalus alone Chthamalus fundamental niche low middle high Location in intertidal zone

Chthamalus realized niche Competition and Limitation of Resources How can we determine the realized niche of each barnacle? Where do they grow when allowed to compete? Balanus Chthamalus growth rate Balanus realized niche Chthamalus realized niche low middle high Location in intertidal zone

Competitive Exclusion Principle Two species cannot coexist if they occupy the same niche (the barnacles did not coexist where their fundamental niches overlapped) Competition between two species with identical niches results either in competitive exclusion or the evolution of resource partitioning Stable coexistence requires niche differentiation, members of each species compete more strongly among themselves than with members of the other species (intraspecific > interspecific)

Avoiding Competition Resource partitioning sympatric species consume slightly different foods or use other resources in slightly different ways Character displacement sympatric species tend to diverge in those characteristics that overlap Ex: Anolis lizard sp. perching sites in the Dominican Republic Ex: Darwin’s finch beak size on the Galapagos Islands

Resource Partitioning

Competition: a closer look Interference~ actual fighting over resources Exploitative~ consumption or use of similar resources Competitive Exclusion Principle (Lotka / Volterra)~ 2 species with similar needs for the same limiting resources cannot coexist in the same place

interspecific competition Gause Experiment two species of Paramecium predict the outcome of interspecific competition P. aurelia P. caudata Competitive exclusion When forced to compete, one species eliminates other

Species Diversity 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 Species Exerts strong control on the community structure The affect on its community or ecosystem is much larger and more influential than would be expected from mere abundance. Often large predators Critical 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.

How Keystone Species Affect Community Structure Starfish Pisaster preditor How do starfish promote coexistence? competitors Barnacles Mussels Balanus Mytilus Starfish are picky – they prefer to eat mussels (dominant competitor), allowing barnacles (weaker competitor) to coexist.

Removal experiment - mussels are the dominant competitor - competitive exclusion of barnacles starfish removed mussels % of inter- tidal zone barnacles time

GENERALIST VS SPECIALIST Animals are generally selective and efficient in their food choices Some animals, such as gulls, are feeding “generalists” Other animals, such as koalas, are feeding “specialists”

GENERALIST VS SPECIALIST narrow diet specialist consumes only one prey type broad diet generalist consumes many prey types

GENERALIST VS SPECIALIST Generalists - Broad niche When generalists and specialists collide, generalists usually win Specialists - Narrow niche

Invasive Species Invasive species competitively exclude native species Imported fire ant Kudzu Purple loosestrife Zebra mussel Squirrels

Ecosystem Change: Succession Succession - orderly, natural changes that take place in communities of an ecosystem over time. Pioneer species: first organisms to live in a new habitat. Tend to be small, fast growing plants, lichens, fungus. Increase soil and make the ground more hospitable for other species.

Ecosystem Change Constant state of change Disturbance influences species diversity and composition Storm, fire, flood, human activity changes a community by removing organisms or changing resource availability Not necessarily bad

Ecosystem Change Intermediate disturbance hypothesis Moderate levels of disturbance create conditions that foster greater species diversity than low or high levels of disturbance

Primary Succession Primary succession is colonization by communities of organisms where life has not existed before.

Terrestrial Primary Succession

Secondary Succession Secondary succession is the sequence of community changes that occur when a community is disrupted by natural disasters or human actions.

Climax Community The final stable plant community is called a climax community.   This community may reach a point of stability that can last for hundreds or thousands of years.

Ecosystem Stability The interrelationships and interdependencies of organisms affect the development of stable ecosystems – in other words the homeostasis of ecosystems.

Tolerance Tolerance is the ability to withstand fluctuations in biotic and abiotic environmental factors. Biodiversity gives an ecosystem more tolerance. The greater the biodiversity, the healthier the ecosystem.

Island Biogeography Because of their isolation and limited size, islands are natural laboratories for studying bio-geographical factors Also applies to islands of land such as national parks or preserves.

Island Biogeography Two factors Rates of immigration and extinction are influenced primarily by the size of the island and the distance of the island from the mainland. The greater the size of the island, the higher the immigration rates and lower the rates of extinction. As the distance from the mainland increases, the rate of immigration falls, whereas extinction rates increase