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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
II. Species Interactions:
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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II. Species Interactions:
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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II. Species Interactions:
B. Predation
II. Species Interactions:
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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II. Species Interactions: Competit ion
and Predation
Preys chemical warfare:
II. Species Interactions: Competit ion
and Predation
Preys Coloration:
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II. Species Interactions: Competit ion
and Predation
Preys mimicry:
II. Species Interactions:
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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II. Species Interactions:
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
II. Species Interactions:
Mutualism:Protection.
D. Mutualism: Food supply
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II. Species Interactions:
E. Commensalism:
It is an interaction that benefits onespecies but has little or no effects on theother species.
Example: The birds and the tree
II. Species Interactions:
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
IV. Population Dynamics
A. Population Distribution: 3 patterns
Random Dispersion
Clumping uniformdistribution
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IV. Population Dynamics
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
IV. Population Dynamics
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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IV. Population Dynamics
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.
IV. Population Dynamics
C. Age structure:
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Logistic Growth of a Sheep Population on
the island of Tasmania, 18001925
IV. Population Dynamics
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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IV. Population Dynamics
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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V. Reproductive Patterns
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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V. Reproductive Patterns