Ecosystems Structure and Dynamics Community Ecology The scientific study of interactions among organisms and between organisms and their environments.

Ecosystems: Everything Is Connected Everything in an ecosystem is connected. What affects one part of an ecosystem often affects many other parts of the ecosystem as well.

Organisms and Species An organism is a single living thing. An organism is a single living thing. A species is a group of organisms that can produce fertile offspring with the same characteristics. A species is a group of organisms that can produce fertile offspring with the same characteristics.

Populations A population is a group of organisms from the same species living in the same place. A 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. There may be thousands of populations for any particular species.

The Community A group of populations of different species living close enough to interact A group of populations of different species living close enough to interact Interspecific interactions = all the species in a given area.

Some habitats Forest Tree Lake or pond City park Cave Fen or swamp or marshland Reef Habitat Any place within the ecosystem where a population or community lives where a population or community lives

 Species  Population  Community  Ecosystem  Biome  Biosphere Levels of Organization Biome

Interaction in Communities Community interactions are classified by whether they help, harm, or have no effect on the species involved. 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 competition Competition Shapes Communities

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

How Species Interact With Each Other Ecosystems work best when every in it is filled. Ecosystems work best when every niche in it is filled. Species interact with each other in many ways. The most common relationships are: Species interact with each other in many ways. The most common relationships are: 1.Predation 2.Competition 3.Parasitism 4.Mutualism 5.Commensalism

Central to Competition and Community Habitat & microhabitat (Space utilization) Habitat & microhabitat (Space utilization) Food “spectrum,” essential nutrients Food “spectrum,” essential nutrients Reproductive requirements Reproductive requirements Nutrition, nest/den sites Nutrition, nest/den sites Seasonality: When are resources required, used Seasonality: When are resources required, used 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 The Ecological Niche

Predation In predation, one organism eats another. In predation, one organism eats another. The animal that kills and eats is the predator. The animal that kills and eats is the predator. The animal that is eaten is the prey. 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. 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. 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. This creates a specific cyclical relationship between predators and prey.

Predation Hare cycles may be caused by increasing food shortages during winter caused by overgrazing Or they may be due to predator-prey interactions Cycles could be affected by a combination of food resource limitation and excessive predation Predators 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. +/- 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. 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. A plant’s main protective devices are chemical toxins, spines, and thorns.

Interaction By Symbiosis Two organisms living together in close association.Two organisms living together in close association.

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

Tick Tapeworm Parasitism Parasitism is a relationship between two organisms in which one feeds off another. 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 feeds off the other is the parasite. The organism that contains the parasite is the host. 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. 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 harmed mites hitching a ride on a beetle

Population Niche Fundamental niche Fundamental 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 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 growthrate Location in intertidal zone lowhighmiddle Chthamalus alone Balanus alone How can we determine the fundamental niche of each barnacle? Removal experiments – remove each species and see where the other grows Balanusfundamentalniche Chthamalus fundamental niche

growthrate Location in intertidal zone lowhighmiddle How can we determine the realized niche of each barnacle? Where do they grow when allowed to compete? Balanusrealizedniche Chthamalus realized niche BalanusChthamalus Competition and Limitation of Resources

Two species cannot coexist if they occupy the same niche ) Law of Competitive Exclusion No two species can occupy the same niche and compete for exactly the same resources for an extended period of time. No 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. 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. Given resource can only be partitioned a finite number of times.

Avoiding Competition Resource partitioning sympatric species consume slightly different foods or use other resources in slightly different ways 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 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

Biodiversity Measures the number of different species in the community (species richness) and the relative abundance of each species. 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. 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 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. 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.

Barnacles Mussels Balanus Mytilus StarfishPisaster Starfish 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 Structure preditor competito rs

Removal experiment time starfishremoved %ofinter-tidalzone mussels