Community EcologyCommunity Ecology

Chapter 8Chapter 8

Shohail ChoudhuryShohail Choudhury

Community StructureCommunity Structure

Ecologists use three characteristics to describe a Ecologists use three characteristics to describe a biological community.biological community.

1.1. Physical appearancePhysical appearance: the relative sizes, stratification, : the relative sizes, stratification, and distribution of its populations and speciesand distribution of its populations and species

2.2. Species diversitySpecies diversity: a combination of numbers of : a combination of numbers of different species (richness) and abundance of different species (richness) and abundance of individuals within each species (species evenness)individuals within each species (species evenness)

3.3. Niche structure:Niche structure: the number of ecological niches, the number of ecological niches, their resemblance or difference from each other, and their resemblance or difference from each other, and interaction of species with each otherinteraction of species with each other

Species DiversitySpecies Diversity

Factors: LatitudeFactors: Latitude PollutionPollution

Ants Birds

Species on IslandsSpecies on Islands

The number of species on an island is determined by: The number of species on an island is determined by: how fast new how fast new species arrivespecies arrive, , how fast old species how fast old species become extinctbecome extinct, , the the sizesize of the island, of the island, and the and the distancedistance from the mainland. from the mainland.

This model has been This model has been expanded to include expanded to include habitat islands in habitat islands in protected areas such protected areas such as national parks.as national parks.

Types of SpeciesTypes of Species Species in a community play many different roles in its Species in a community play many different roles in its

ecology.ecology.

Types of SpeciesTypes of Species1.1. Native speciesNative species are those whose original home is in are those whose original home is in

this particular ecosystem.this particular ecosystem.

2.2. Nonnative speciesNonnative species originally evolved in a different originally evolved in a different ecosystem and migrated or were introduced to a ecosystem and migrated or were introduced to a new ecosystem.new ecosystem.

3.3. Indicator speciesIndicator species alert us to harmful changes taking alert us to harmful changes taking place in biological communities.place in biological communities.

– Birds are excellent biological indicators because Birds are excellent biological indicators because they are everywhere and are quickly affected they are everywhere and are quickly affected

b.b. Some amphibians are also considered indicator Some amphibians are also considered indicator species.species.

Types of SpeciesTypes of Species

Keystone species:Keystone species: help ecological communities run help ecological communities run smoothly; they determine the type and number of smoothly; they determine the type and number of community species. community species.

Loss of a keystone species has far-reaching Loss of a keystone species has far-reaching ramifications for other species in a community ramifications for other species in a community (for example, alligators).(for example, alligators).

Foundation speciesFoundation species shape communities by shape communities by creating and enhancing habitat that benefits creating and enhancing habitat that benefits other species.other species.

Elephants, in breaking and uprooting trees, Elephants, in breaking and uprooting trees, create forest openings. Grazing species benefit. create forest openings. Grazing species benefit. The rate of nutrient cycling is increased.The rate of nutrient cycling is increased.

Species InteractionsSpecies Interactions

Five basic species interactions are Five basic species interactions are competition, predation, competition, predation, parasitism, mutualism, parasitism, mutualism, andand commensalism commensalism..

A.A. Competition between species for food, sunlight, water, Competition between species for food, sunlight, water, soil, space, nest sites, etc. is interspecific competition.soil, space, nest sites, etc. is interspecific competition.

1.1. With intense competition for limited resources, one With intense competition for limited resources, one species must migrate, shift its feeding habits/behavior, species must migrate, shift its feeding habits/behavior, or face extinction.or face extinction.

2.2. As humans take more and more space, other species As humans take more and more space, other species are compromised.are compromised.

Some species evolve Some species evolve adaptationsadaptations to to reduce/avoid competition for reduce/avoid competition for resources.resources.

1.1. Resource partitioning. Resource partitioning. Eg. Eg. Owls hunt at night; hawks hunt Owls hunt at night; hawks hunt

during the dayduring the day..

PredationPredation

• Predator–prey relationships define one species (the Predator–prey relationships define one species (the predator) predator) feeding/preying on anotherfeeding/preying on another. .

• Individually prey is harmed, but Individually prey is harmed, but predation can helppredation can help the the population by eliminating the sick, weak, and old.population by eliminating the sick, weak, and old.

• Predators have a variety of ways to capture prey. Predators have a variety of ways to capture prey.

• Prey species escape predators in a number of different Prey species escape predators in a number of different ways, such as ways, such as swift movement, protective shells, swift movement, protective shells, camouflage, or use of chemicals to repel or poison.camouflage, or use of chemicals to repel or poison.

Parasitism, Mutualism, and CommensalismParasitism, Mutualism, and Commensalism

Parasites Parasites live on or in another species. live on or in another species. The host is harmed, but the parasite contribute to biodiversity The host is harmed, but the parasite contribute to biodiversity by controlling the species populations. by controlling the species populations.

MutualismMutualism is a relationship that benefits both species; Mutualism is is a relationship that benefits both species; Mutualism is not cooperation; each species exploits the other.not cooperation; each species exploits the other.

a.a. Birds, African buffalo, elephants, and rhinocerosesBirds, African buffalo, elephants, and rhinocerosesb.b. Clownfish and anemonesClownfish and anemones

Some species interaction helps one species but does nothing for Some species interaction helps one species but does nothing for the other; this is the other; this is commensalism. commensalism. Ex: Redwood sorrel (herb)Ex: Redwood sorrel (herb)

Ecological SuccessionEcological Succession

With new environmental conditions, community With new environmental conditions, community structures can change; structures can change; one group of species is one group of species is replaced by anotherreplaced by another. .

Primary ecologicalPrimary ecological succession is the gradual succession is the gradual establishment of biotic communities on lifeless establishment of biotic communities on lifeless ground. ground.

Primary succession can also take place in newly created Primary succession can also take place in newly created small small pondsponds that, over a long period of time, will be that, over a long period of time, will be transformed transformed to a marshto a marsh and finally and finally to dry landto dry land..

Communities in TransitionCommunities in Transition

Primary SuccessionPrimary Succession

Secondary ecological successionSecondary ecological succession

A series of communities with different species A series of communities with different species developing in places developing in places with soil or bottom sedimentwith soil or bottom sediment. .

The soil or sediment remains after the natural The soil or sediment remains after the natural community of organisms has been disturbed, community of organisms has been disturbed, removed, or destroyed.removed, or destroyed.

a.a. Forest fires or Forest fires or deforestationdeforestation, for example, can convert , for example, can convert a particular stage of succession to an earlier stage.a particular stage of succession to an earlier stage.

b.b. Changes in vegetation during secondary succession Changes in vegetation during secondary succession also change the numbers and types of animals and also change the numbers and types of animals and decomposers.decomposers.

Secondary SuccessionSecondary Succession

150-200 yrs150-200 yrs

Ecological Stability, and SustainabilityEcological Stability, and Sustainability

Living systems maintain some degree of stability or Living systems maintain some degree of stability or sustainability through constant changesustainability through constant change in response to in response to changing environmental conditions.changing environmental conditions.

All systems are constantly changing. All systems are constantly changing. There are a series of positive and negative loops that There are a series of positive and negative loops that

interact to provide stability or sustainability over the interact to provide stability or sustainability over the life span of a system. There are three aspects of life span of a system. There are three aspects of stability or sustainability in living systems.stability or sustainability in living systems.

1.1. Resists being disturbed : have Resists being disturbed : have persistence or inertiapersistence or inertia..2.2. Can keep its numbers within limits: shows Can keep its numbers within limits: shows constancyconstancy..3.3. Able to repair damage : shows Able to repair damage : shows resilienceresilience..

See any element of Debate?

Debate?Debate?

• 1.1. Some developers feel there is Some developers feel there is no good reason to no good reason to maintain biological diversitymaintain biological diversity if it does not necessarily if it does not necessarily lead to ecological stability.lead to ecological stability.

• 2.2. Ecologists point out that environmental Ecologists point out that environmental degradation is and has been occurring degradation is and has been occurring due to human due to human disturbancesdisturbances. This has disrupted some of the . This has disrupted some of the environmental services that support and sustain all environmental services that support and sustain all life and all economies.life and all economies.

• The wise course is to use caution regarding the The wise course is to use caution regarding the making of potentially harmful changes to making of potentially harmful changes to communities and ecosystems.communities and ecosystems.

Population EcologyPopulation Ecology

Chapter 9 Chapter 9

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