Env200 Chap 2 Community Ecology and Population Ecology

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Community Ecology and

Population Ecology

Chapter 2

Chapter Outline

I. Types of Species

II. Species Interactions

III. Ecological Stability andSustainability

IV. Population DynamicsV. Reproductive Patterns


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I. Types of Species

A biological community is shaped by the

individual species that live in it. Any species

may play one or more than one role in this

community. Species can be:

Native Species vs Nonnative Species

Indicator Species

Keystone Species

Foundation Species

I. Types of Species

A. Native Species vs Nonnative Species:

Species that normally live and thrivein aparticular community.

Species that migrate into or deliberately oraccidentally are introduced into acommunity are called nonnative or

invasive or alien species Nonnative species are not necessarily

villains


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I. Types of Species

B. Indicator Species: Species that serve as an early warning of

damage to a community or an ecosystem

Example: Trout in freshwater

I. Types of Species

Amphibian species decline in many parts ofthe world. This may indicate severe decline inenvironmental quality that supports their lifecycles.

Indicator

Species


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II. Types of Species

B. Indicator SpeciesPopulation of various frog species can

decline due to the effects of harmfulenvironmental alterations at differentpoints in their life cycle, such as:

Habitat loss

Prolonged drought

Parasites and viral or fungal diseases

Climate change and increase in ultraviolet

radiation Over hunting

Natural immigration

I. Types of Species

C. Keystone Species:

They determine the type and number of other speciesin a given community

Eliminating a keystone species may dramatically alterthe structure, and function of a community.

Ecological roles of a keystone species:

Pollination

Top predating

Soil aeration


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I. Types of Species

D. Foundation Species

Can create and enhance habitats that canbenefit other species in a community

Some ecologists think that keystone speciescategory should expand to include foundationspecies as well.

Elephants create forest

openings in the savanna

and woodlands of Africa.

II. Species Interactions: Species interactions play important roles in

biological communities.

When different species live in a certain

community, they have activities and

resources to share among each others.

This might trigger communication and

interaction; leading to possible positive

influence, negative, or no impairment. Species interactions play important roles in

population control

They illustrate an important principle ofsustainability.


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II. Species Interactions:

Species can interact through:

A. Competition

B. Predation

C. Parasitism

D. Mutualism

E. commensalism


A. Competition

It is the most common interactionbetween species mostly competition forfood and space.

No two species can share the same vitaland limited resource for long.

Consequences = resource partitioning Example: humans, lions and leopards, hawks

and owls


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A. Competition

Reducing or avoiding competition can occurthrough: resource partitioning

Fig. 5-8, p. 107

Cape May

Warbler

Stepped Art

Blackburnian

Warbler

Black-throated

Green Warbler

Yellow-rumped

Warbler

Bay-breasted

Warbler

Each species minimizes competition for food with theothers by spending at least half of its feeding time ina distinct portion of the tree and by consumingdifferent insect species.


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B. Predation


B. Predation

Member of one species (predator) feedsdirectly on all or part of a living organismor another species (prey).

Together, hunter and hunted form apredator-prey relationship

At individual level, the prey is harmed

At the population level, predationbenefits evolution of preys by naturalselection


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II. Species Interactions: Predation

How predatorsincrease theirchances of getting ameal?

By using their senses

Herbivores: walk,swim, or fly to theplants they feed on

Carnivores: pursuit orambush

Use of chemicals toattack (spiders,poisonous snakes)

How do preys defendagainst predators?

Highly developed sensesand abilities (run, swim,fly fast, smell)

Protective shells(turtles), or spines(porcupines)

Camouflage

Chemical warfare (badtasting, bad smelling)

Coloration

Living in large groups.

II. Species Interactions: Competit ion

and Predation

Preys Camouflage:


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and Predation

Preys chemical warfare:


and Predation

Preys Coloration:


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and Predation

Preys mimicry:


C. Parasitism: It is when one species (parasite) feeds on

part of another organism (host).

The parasite benefits and the host is harmed

It can be viewed as a special form ofpredation with the parasite much smaller thanthe host and rarely kills it.

From the host point of view, parasites areharmful, yet they promote biodiversity andcontrol populations

Parasites live inside, outside, or even havelittle contact with their hosts.


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D. Mutualism:

It is a win to win relationship.

It is when two species or a network of speciesinteract in a way that benefits both; or inother words, each species benefits byexploiting the other.

Examples of benefits:

Pollination Food supply

Protection


Mutualism:Protection.

D. Mutualism: Food supply


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E. Commensalism:

It is an interaction that benefits onespecies but has little or no effects on theother species.

Example: The birds and the tree


E. Commensalism:the Epiphytes plantattach itself to thetrunk of a big treeto benefit from asolid base, have

better access tosunlight, water,humid air, andnutrients fallingfrom the upper tree.


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III. Ecological Stabil ity and

Sustainability

Living systems maintain some degree ofstability through constant changein responseto environmental conditions through:

Inertia or persistence that is the ability of aliving system to resist being disturbed oraltered

Constancy that is the ability of a livingsystem to keep its numbers within the limitsimposed by the available resources.

Resilience that is the ability of a livingsystem to bounce back and repair damageafter a non drastic disturbance

III. Ecological Stabil ity and

Sustainability

Having many different species appears toincrease the sustainability of manycommunities

Human activities are disrupting

ecosystem services that support andsustain all life and all economies.


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IV. Population Dynamics

Population dynamics is the study of why andhow population change in their:

distribution,

number,

age structure,

and density

in response to changes in the environmental

conditions


A. Population Distribution: 3 patterns

Random Dispersion

Clumping uniformdistribution


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B. Changes in Population Size:

Populations increase through births andimmigration and decrease through death andemigration.

C. Age structure:

It is how fast a population is able to grow or

decline depending on its age structure.

Proportions of individuals at various ages

determine the size of a population: Pre-reproductive age Reproductive age

Post-reproductive age


C. Age structure:

No population can increase its size indefinitely.

Biotic Potential: capacity of a population forgrowth.

Intrinsic rate of increase: (r), rate at whicha population would grow if given unlimitedresources.

Environmental resistance: all factors thatact to limit the growth of a population

Carrying Capacity: (k), Maximum populationof a given species that a particular habitat cansustain indefinitely without being degraded


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C. Age structure:

Exponential Growth: with ample resourcesa population can grow exponentially. Thegrowth starts slow then accelerates as thebase size of the population increases.

(j shaped growth curve).

Logistic Growth: is the rapid exponentialgrowth followed by a steady decrease inpopulation with time until the population sizelevels stop.


C. Age structure:


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Logistic Growth of a Sheep Population on

the island of Tasmania, 18001925


C. Age structure:

Exceeding the carrying capacity: somespecies do not make a smooth transitionbetween exponential growth and logistic growthdue to resource over

consumption.

Birth rate drops,

death rates rise,

the population suffers

from dieback.


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D. Population Density:

It is the number of individuals in a populationfound in an area or a volume.

Density dependent population control factors:

Sexual reproduction (more mates but also morecompetition)

Resources availability (food, water, space,sunlight)

Protection from predators Transmission of infectious diseases

V. Reproductive Patterns

Asexual Reproduction: offspring are an exactgenetic replica of a single parent. Ex: corals,bacteria

Sexual Reproduction: offspring are a mixingof the genetic material of two individuals

Disadvantages: Males do not give birth

Increased chance of genetic errors

Mating rituals are time and energy consuming

Advantages: Genetic diversity in offspring

Parents provide food, protection, and training toyoungsters.


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r-selected species: species with a capacity ofhigh rate of population increase. These havemany, small offspring and give them little or noparental protection. Ex: bacteria, algae,rodents, insects. These species are calledopportunists.

K-selected species: or competitors, theyreproduce later in life and have small numberof offspring. They do generally well incompetitive conditions. Ex: mammals, trees,birds those with long generation time and lowreproduction rate are prone to extinction.


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Env200 Chap 2 Community Ecology and Population Ecology

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