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Ecology Biological Communities

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Presentation on theme: "Ecology Biological Communities"— Presentation transcript:

1 Ecology Biological Communities
NO species exists independently of other species

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

3 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

4 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

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

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

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

8 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

9 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

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

11 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.

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

13 Cryptic Coloration Prey may evolve to blend in too! Camouflage

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

15 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

16 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

17 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

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

19 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.

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

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

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

23 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

24 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

25 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

26 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?

27 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

28 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

29 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)

30 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

31 Resource Partitioning

32 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

33 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

34 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.

35 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.

36 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.

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

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”

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

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

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

42 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.

43 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

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

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

46 Terrestrial Primary Succession

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

48 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.

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

50 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.

51 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.

52 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


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