Transcript Population Ecology-Chapter 14 PowerPoint

Population Dynamics
Chapter 14: Population Ecology
Characteristics of Populations
• Habitat
– Place where an organism or species normally
lives
• Species
– Organisms that are able to interbreed with
one another to produce fertile offspring
– Resemble one another in appearance,
behaviour, chemistry and genetic make-up
– Mule-not a species but a hybrid (donkey and
horse)
Characteristics of Populations-cont’d
• Population size
– Number of individuals of a species occupying
a given area/volume at a given time
• Population density (D)
D=N
S
N: Total number of individuals
S: Space occupied by the population
• Small organisms usually have higher
population densities than larger organisms
Characteristics of Populations-cont’d
• Crude density
– Population density measured in terms of the
number of organisms of the same species
within a habitat’s total area
• Ecological density
– Population density measured in terms of the
number of organisms of the same species
within the area actually used by those
organisms (ex. land animals do not live in
lakes)
Characteristics of Populations-cont’d
• Population dispersion patterns vary by
species within a habitat (fig. 4, page 652)
– Clumped dispersion (ex. schools of fish)
– Uniform dispersion (ex. King penguins)
– Random dispersion (ex. rainforest trees)
• Rarely found in nature
Characteristics of Populations-cont’d
• It is often impractical to count exact
numbers of individuals in a population
– Biologists resort to counting a sample of the
population at a particular time and then use
this number to estimate total size
– There are three main sampling techniques:
• Quadrat sampling
• Mark-recapture method
• Technological tracking devices
Characteristics of Populations-cont’d
• Quadrat sampling
– Used for stationary or small organisms (ex.
plants, insects)
– A quadrat (a defined area/frame; ex. 1m2) is
used and samples of one or more populations
is counted within that area
– Population size and density can be
determined based on that quadrat’s data,
which can be extrapolated for the entire area
Characteristics of Populations-cont’d
• Mark-Recapture Method
– Used for mobile wildlife populations (ex. fish,
bears)
– A sample of animals is captured, marked in
some way and then released
– Those organisms are allowed to mix randomly
with unmarked animals and after a period of
time, a second sample of animals is captured
• The proportion of marked to unmarked animals in
this sample can be used to estimate the size of the
entire population
Characteristics of Populationscont’d
• Mark-Recapture Method-cont’d
M=m
N n
M = Total # marked
N = Total population
m = # of recaptures
n = Size of 2nd sample
Characteristics of Populations-cont’d
• Technological Tracking Devices
– When capturing animals for estimating
population size, researchers may also attach
radio collars, satellite-linked devices or other
technological equipment
• Used to track migration and/or behaviour patterns
• Information can be mapped in geographic
information systems (GIS)
• Must ensure these devices do not harm the
animals or restrict their activities
Measuring and Modeling
Population Change
• Resources available to individuals in a
population are finite and can be biotic
(living) or abiotic (non-living)
• Carrying capacity
– The maximum number of organisms that can
be sustained by available resources over a
given period of time (aka biocapacity)
Measuring and Modeling
Population Change
• Population dynamics
– Changes in population characteristics determined by
natality, mortality, immigration and emigration
• Fecundity
– The potential for a species to produce offspring in one
lifetime (ex. high fecundity-starfish; low fecundityhumans)
– Fertility is often significantly less than this due to food
availability, mating success, disease, migration
Measuring and Modeling
Population Change
• Biotic potential
– The maximum rate a population can increase
under ideal conditions (ex. E. coli can double
every 12 minutes)
• Population change =
[(births + immigration)-(deaths + emigration)] x 100
initial population size (n)
Measuring and Modeling
Population Change
• Open population
– Size and density influenced by births, deaths, immigration
and emigration
– Most wild populations are open
• Closed population
–
–
–
–
–
Size and density Influenced by births and deaths only
No migration occurs
Rarely found in nature (ex. isolated animals on an island)
Laboratory settings are closed
Mark-recapture sampling (due to short time frame
between samples)
Measuring and Modeling
Population Change
• Three general survivorship patterns of species:
Type I: High survivorship until fairly late in life, then high mortality
Typically produce small numbers of offspring
Type II: A fairly constant death rate
Type III: Low survivorship early in life (ex. green sea turtles)
Typically produce large numbers of offspring
Measuring and Modeling
Population Change
• Geometric growth
– For many species, while deaths can occur
throughout the year, births are restricted to a
particular time of the year (breeding season)
• Population grows rapidly during breeding season
then declines throughout the rest of the year until
the next breeding season
– Growth rate is a constant from year to year
but not during the year
Measuring and Modeling
Population Change
• Geometric growth-cont’d
Measuring and Modeling
Population Change
• Exponential Growth
– A wide variety of species are able to reproduce at a
fixed rate on a continuous basis
– Doubling time is a constant value
– Populations exhibiting this growth increase in
numbers rapidly
– Results in a J-shaped growth curve
– Although the overall graph appears similar to
geometric growth (J-shape), in this case, there are no
fluctuations (jumps) as a result of breeding times
Measuring and Modeling
Population Change
• Exponential growth-cont’d
Measuring and Modeling
Population Change
• Logistic Growth
– Most common growth pattern seen in nature
– Geometric and exponential models of
population growth assume that a population
will grow indefinitely at the same rate
• Realistically, food, water, light and space in the
ecosystem become factors that limit population
growth as resources are consumed and the
population nears the ecosystem’s carrying capacity
• At the carrying capacity, the number of births and
the number of deaths become equal
Measuring and Modeling
Population Change
Logistic Growth-cont’d
Measuring and Modeling
Population Change
• Logistic Growth-cont’d
– S-shaped (sigmoidal) curve
– Three distinct phases:
• Lag phase: Population is small and increasing
slowly
• Log phase: Population undergoes very rapid
growth
• Stationary phase: Population growth slows as the
population experiences environmental resistance.
Occurs at or close to the carrying capacity.
Population is at dynamic equilibrium
(births=deaths) and no net increase in numbers
occurs.
Factors Affecting Population Change:
Density-Dependent Factors
• Density-Dependent Factors
– Play a greater role in limiting population
growth as the population increases in size
– Ex. competition, predation, disease
• Intraspecific competition
– When the individuals of a population of the
same species compete for the same
resources
• Growth rate slows as the population increases
• Can reduce the number of offspring born
Factors Affecting Population Change:
Density-Dependent Factors
• Predation
– A carnivorous predator (of one species)
catches, kills and consumes prey (of another
species)
– Some predators prefer one type of prey over
another if that prey has a larger population
and is easier to catch
• Helps to regulate the number of preferred prey
Factors Affecting Population Change:
Density-Dependent Factors
• Disease
– In dense or overcrowded populations,
pathogens are able to pass more easily from
host to host, since there are more hosts close
together
• Population deceases in size due to increased
mortality
Factors Affecting Population Change:
Density-Dependent Factors
• Allee Effect
– When population numbers become so low
that the species cannot reproduce fast
enough to offset mortality
• Mates are difficult to find since there are so few
individuals
• Population usually does not survive; especially
harmful to threatened species
Factors Affecting Population Change:
Density-Dependent Factors
• Minimum viable population size
– The smallest number of individuals needed to
ensure a population can continue for a given
period of time
• Population can cope with variations in natality and
mortality, as well as environmental changes or
disasters
• Population maintains enough genetic variation
amongst its members
Factors Affecting Population Change:
Density-Independent Factors
• Density-Independent Factors
– Play a role in limiting population growth
regardless of population size
– Ex. extreme weather, human intervention
• Ex. Thrips (insect) have lower reproductive
success at lower temperatures
• Insecticide application (can result in death
directly or through biomagnification)
Factors Affecting Population Change:
Density-Independent Factors
• Limiting Factor
– The essential resource that is in shortest
supply or unavailable
– Determines how much the individual or
population can grow (affects the biotic
potential)
– Ex. light, space, water, nutrients
Interactions Within Communities
• Community
– Made up of all populations of different species
within an ecosystem
• Interspecific competition
– When the individuals of different species
compete for the same resources
– Restricts population growth
– A driving force for populations of species to
evolve adaptations to continue to use resources
Interactions Within Communities
• Ecological Niche (organism’s “occupation”)
– An organism’s biological characteristics, including the
use of, and interaction with abiotic and biotic
resources in its environment
• Fundamental Niche
– An organism’s biological characteristics and the set of
resources individuals in the population are
theoretically capable of using under ideal conditions
• Ex. If resources were abundant and no competition
existed
Interactions Within Communities
• Realized Niche
– An organism’s biological characteristics and the set of
resources individuals in the population actually use
under existing environmental conditions
• Symbiosis
– Two species maintain a close, usually physical
association
– At least one of the species benefits
– Includes mutualism, commensalism and parasitism
Interactions Within Communities
• Types of Interspecific Competition
– I. Interference competition: Involves fighting
over shared resources by individuals of
different species
– II. Exploitative competition: Involves
consumption of shared resources by
individuals of different species
• May limit resource availability to another species
Interactions Within Communities
• Interspecific Competition
– Strongest competition occurs between
populations of species that experience niche
overlap
– Competition declines due to 3 possible outcomes:
• Population size of the weaker competitor declines
• One species may change its behaviour so that it
survives on different resources
• Individuals of one population may migrate to another
habitat where resources are more plentiful
Interactions Within Communities
• Resource partitioning
– Avoidance of, or reduction in, competition for
similar resources by individuals of different
species occupying different non-overlapping
ecological niches
– Ex. Anolis lizards partition their tree habitats
by occupying different perching sites
– Ex. plants differing in their root systems to
allow them to acquire water and mineral ions
from the same environment
Interactions Within Communities
• Predation
– Type of interspecific interaction
– Population density of one species (predator)
increases while the population density of the
other species (prey) decreases
– A cyclical relationship: population of prey
increases; more food for predators and its
population increases; food (prey) starts to
decrease resulting in decrease in predator
population; less predators allows the prey
population to increase once again
• If other prey is available, it alters this relationship
Interactions Within Communities
Interactions Within Communities
• Canadian lynx-snowshoe hare cycle (10 years)
Interactions Within Communities
• Defence Mechanisms
– Evolved due to repeated encounters with
predators over time
• Have initiated the evolution of counter-adaptations
in some predators
– Plants: morphological defences (thorns,
hooks, spines, needles) and chemical
defences (distasteful, toxic)
– Insects: some use chemicals produced by
their food as protection from their predators
(ex. monarch butterfly)
Interactions Within Communities
• Passive Defence Mechanisms
– Ex. Hiding
– Ex. Camouflage
– Ex. Visual warning (ex. rings) to predators of
chemical defences (poisons)
– Ex. Mimicry
• Batesian: a harmless species mimics a harmful
species (ex. Viceroy butterflies mimic monarch
butterflies)
• Mullerian: several unrelated species resemble one
another and are all harmful (minimizes predation)
Interactions Within Communities
• Active Defence Mechanisms
– Ex. Fleeing from predators
– Ex. Alarm calls (prey mobs the predator)
– More costly in terms of energy required
Interactions Within Communities
• Types of Symbiotic Relationships:
– Mutualism (+/+)
• Both organisms benefit
• Neither organism is harmed
• Ex. bacteria in our intestinal tract (they get
nutrients from the food we consume and produce
vitamins that we need)
• Ex. pollination (insects and animals ingest
pollen/nectar, and pollen stuck to bodies of insects
and animals gets spread to other flowers)
• Obligatory mutualism: neither species can survive
without the other
Interactions Within Communities
– Commensalism (+/0)
• One organism benefits and the other organism is
unaffected
• Ex. remora (small fish) attach themselves to sharks and
feed on small pieces of the shark’s prey and get free
transportation
– Parasitism (+/-)
• One organism (parasite) benefits at the expense of the
other organism (host)
• Host is harmed but is usually not killed
• ~1/4 animal species is thought to be a parasite
• Ex. Plasmodium (malaria), tapeworms, fleas, lice
• Social parasite: manipulates the social behaviour of
their hosts to complete their life cycle (ex. cowbirds use
nests of smaller birds and these smaller bird newborns
are usually killed)
Interactions Within Communities
• Introduction of Exotic (non-indigenous) Species
– Can disrupt ecosystems’ dynamic equilibrium and
displace indigenous species to such a degree that
they impact on the biodiversity in that ecosystem
– Since non-indigenous species often have few
predators in that area, they can reduce or eliminate
indigenous species by outcompeting them for food
and habitat, or by preying on them
– Ex. European rabbit in Australia (page 686)
– Ex. West Nile virus (from Uganda) is believed to have
been introduced into North America accidently via an
exotic frog species