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Chapter 5
Biodiversity, Species Interactions
and Population Control
Species Interact in major ways
Interspecific competition – 2 or more species
interact to gain access to limited resources
 Predation – prey/predator
 parasitism - parasite/host
 Mutualism – benefits both species
 Commensalism – benefits one species , no effect
on the other
Cyclic changes –
sharp increases in
number followed by
seemingly periodic
 Wolves controlling
deer and moose
 Sheep and rabbits
controlling plant
Role of predation
Competition for resources
the greater the overlap the more intense the
 Resource partitioning –specialized traits allow
species to use shared resources at different times
 Competitive exclusion – intense copetition
between 2 equal species, both suffer (one more
than the other) by having reduced access to
Population Dynamics
characteristics of populations change in response to environmental
Size – number of individuals
Density – number of individuals in a certain space
Distribution – spatial pattern – clumping,uniform dispersion,
random dispersion
Age distribution structure - percentage of individuals in each age
What limits population growth?
Birth, death, immigration, emigration
Population change
= (birth+ immigration) - (death + emigration)
 dependent on resource availability or other
environmental changes
Intrinsic rate of increase®
rate at which a population could grow if it
has unlimited resources
 always limits - light, water, space, nutrients
 “High r” – reproduce early in life, short
generation ie. reproduce many times many
offspring: house fly
Carrying capacity - capacity for
number of individuals of a given species that
can be sustained indefinitely in a given area
 determined by interaction between biotic
potential and environmental resistance
(factors that act jointly to limit a population)
Population Dynamics and Carrying
Basic Concept: Over a long period of time,
populations of species in an ecosystem are
usually in a state of equilibrium (balance
between births and deaths)
– There is a dynamic balance between
biotic potential and environmental
Carrying Capacity (K)
Exponential curve is not realistic due to
carrying capacity of area
 Carrying capacity is maximum number of
individuals a habitat can support over a
given period of time due to environmental
resistance (sustainability)
Biotic Potential
Ability of populations of a given species to
increase in size
– Abiotic Contributing Factors:
 Favorable light
 Favorable Temperatures
 Favorable chemical environment - nutrients
– Biotic Contributing Factors:
 Reproductive rate
 Generalized niche
 Ability to migrate or disperse
 Adequate defense mechanisms
 Ability to cope with adverse conditions
Environmental Resistance
Ability of populations of a given species to
increase in size
– Abiotic Contributing Factors:
 Unfavorable light
 Unfavorable Temperatures
 Unfavorable chemical environment - nutrients
– Biotic Contributing Factors:
 Low reproductive rate
 Specialized niche
 Inability to migrate or disperse
 Inadequate defense mechanisms
 Inability to cope with adverse conditions
Population Density
Population Density (or ecological population
density) is the amount of individuals in a
population per unit habitat area
– Some species exist in high densities - Mice
– Some species exist in low densities - Mountain lions
Density depends upon
– social/population structure
– mating relationships
– time of year
Reproductive Strategies
Goal of every species is to produce as many
offspring as possible
 Each individual has a limited amount of energy to
put towards life and reproduction
 This leads to a trade-off of long life or high
reproductive rate
 Natural Selection has lead to two strategies for
species: r - strategists and K - strategists
r - Strategists
Spend most of
their time in
reproductive life
Minimum life
R Strategists
Many small offspring
 Little or no parental care and protection of offspring
 Early reproductive age
 Most offspring die before reaching reproductive age
 Small adults
 Adapted to unstable climate and environmental conditions
 High population growth rate – (r)
 Population size fluctuates wildly above and below carrying
capacity – (K)
 Generalist niche
 Low ability to compete
 Early successional species
K - Strategists
population at
carrying capacity
K- Strategist
Fewer, larger offspring
 High parental care and protection of offspring
 Later reproductive age
 Most offspring survive to reproductive age
 Larger adults
 Adapted to stable climate and environmental
 Lower population growth rate (r)
 Population size fairly stable and usually close to
carrying capacity (K)
 Specialist niche
 High ability to compete
 Late successional species
Late Loss: K-strategists that produce few young
and care for them until they reach reproductive
age thus reducing juvenile mortality
 Constant Loss: typically intermediate
reproductive strategies with fairly constant
mortality throughout all age classes
 Early Loss: r-strategists with many offspring,
high infant mortality and high survivorship once
a certain size and age
Survivorship curves
proportion of survivors of a
particular species in a particular
age group
a)late loss – type I - elephant
b) early loss – type II songbirds
c) constant loss - intermediate
reproductive strategies- starfish
J-shaped exponential growth
curve, growth
starts slowly then
speeds up
 S - shaped curvelogistic growth
curve - slow start,
rapid exponential
growth, levels off
when K is reached
Population cycles in nature
relatively stable - slight fluctuation above
and below carrying capacity, tropical rain
 erupt - high peak, crash - raccoons
 cyclic - “boom” and “bust”
Effect of population density
on population growth?
Density Independent – floods, drought,
hurricane, habitat destruction, pesticide spraying
 Density dependent – competition for resources,
predation, disease – infectious diseases – plague
in Europe
Communities and ecosystems
respond to environmental change
Primary succession- gradual establishment of
biotic communities in life less areas where there
is no soil in a terrestrial ecosystem or nobottom
sediment in an aquatic ecosystem
 Secondary succession –series of comunities or
ecosystems with different species develop in
places containing soil or bottom sediment
Primary succession
bare rock subject to weathering crumbles into
particles, releasing nutrients
 Pioneer or early successional species (lichens or
mosses)attach to rock and start the process of rock
formation by secreting mild acids
 Mid successional plants – grasses, herbs, small
 Late successional species trees that can tolerate
Secondary succession
ecosystem has been disturbed , removed or
destroyed, some soil or bottom sediment
 abandoned farmland, burned or cut
forests,heavily polluted streams, flooded lands
Living systems are sustained
through constant change
complex system of positive and negative
feedback loops that interact to provide stability
 Inertia or persistence – ability of a living system
such as grassland or forest to survive moderate
 Resilence – ability of a living system to be
restored through secondary succession after a
moderate disturbance
Conservation Biology
 Investigate
human impacts on
 Develop practical approaches to
maintaining biodiversity
 endangered species management,
wildlife reserves, ecological
restoration, environmental ethics
Prevent premature extinction
how ?
 Status
of natural populations,
species in danger of extinction
 Status of the functioning of
 Measures taken to maintain
habitat quality which will support
wild species population
Understand status of
natural populations
 Measure
current population size
 Determine how size will change
with time
 Determine whether populations
are sustainable
Anthropogenic impact
 Fragmenting
or degrading
habitat, simplifying natural
ecosystems, strengthening genetic
resistance to pesticides,
eliminating predators, introduce
alien species, over harvesting,
interfering with nutrient cycles
Working with Nature
 Learn
six features of living systems
– Interdependence
– Diversity
– Resilience
– Adaptability
– Unpredictability
– Limits
Basic Ecological Lessons
Sunlight is primary source of energy
Nutrients are replenished and wastes are
disposed of by recycling materials
Soil, water, air, plants and animals are
renewed through natural processes
Energy is always required to produce or
maintain an energy flow or to recycle
Basic Ecological Lessons
Biodiversity takes many forms because it has
evolved over billions of years under different
Complex networks of + and – feedback loops
Population size and growth rate are controlled
by interactions with other species and with
Organisms generally only use what they need
Four Principles for
We are part of, not apart from, the
earth’s dynamic web of life.
Our lives, lifestyles, and economies are
totally dependent on the sun and the
We can never do merely one thing (first law of
human ecology – Garret Hardin).
Everything is connected to everything
else; we are all in it together.