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Ch. 53: Population Ecology, Ch. 54: Community Ecology - Coggle Diagram
Ch. 53: Population Ecology
Population Size
Factors Effecting Population Size
Population ecology
- study of factors affecting the
size
of a population and how it changes over time.
Population
- group of individuals of a single species living in the same general area.
Populations are described by their boundaries and size.
Adding or removing individuals changes population size.
Factors effecting population size:
Number of births
Number of deaths
Immigration
- individuals moving into a population= :arrow_up: population size
Emigration
- individuals moving out of the population= deaths :arrow_down: populations size
These factors lead to three outcomes of population size:
Reach stable size
Fluctuate irregularly
Rise or fall in a regular pattern
Biotic & Abiotic Factors
Biotic and abiotic factors affect population density, dispersion and demographics.
Population are described by boundaries and size.
Boundaries may be natural (lake or island) or defined by a person (a county).
Density & Dispersion
Density
- number of individuals per unit area or volume.
Ex. # of oak trees per square kilometer within a county.
It is impractical to count all individuals in a population.
Various techniques are used to estimate densities and total population sizes:
-Count # in randomly located plots, then extend to entire area.
-Use # of nests, burrows tracks or droppings to estimate.
Mark-recapture-method
- catch-tag-release method to calculate density.
-Capture, tag, and release a
random sample of individuals (s).
-Give time to mix back in.
-Capture
second sample of individuals (n)
and note
how many of them are marked from first capture (x).
Calculating Population Size
Estimating population size (N)
N=sn/x
Dispersion
- pattern of spacing among individuals within the
boundaries
of the population.
Patterns of Dispersion
Pattern is dispersion if determined by the spacing among individuals within the boundaries of a population.
Clumped Dispersion
Most common
Clumped in areas of
high resource availability
or favorable conditions.
Uniform Dispersion
Evenly spaced
Territoriality
- defense of physical space against other individuals.
Random Dispersion
Unpredictable spacing.
Absence of strong attractions of repulsions among individuals.
Demographics
Demography
- study of statistics of a population and how they change over time.
Biotic and abiotic factors influence birth, death, and migration rates of populations.
Life table
- age-specific summary of the survival and reproductive rates within a population.
Needed:
-# offspring produced by females in each age-group.
-A method for determining the proportion of individuals surviving from one age-group to next.
Survivorship Curve
Survivorship curve
- plot of the proportion or #'s in a cohort still alive at each age.
Shows the pattern of survivorship for ap population.
Three types:
-
Type I
- low death rate early to mid-life; increase in death rate later in life.
Ex. Humans
-
Type II
- constant death rate over time.
Ex. Rodents, lizards
-
Type III
- High death rate for young; decrease in death rate later in life.
Ex. Fish of turtles
Most species are intermediate or show more than one pattern throughout life.
Differ among single specie populations.
Reproductive Rates
Identifies how reproductive output varies with # of breeding females and their ages.
Reproductive output measured as average # of females offspring produced by females within an age group.
Exponential Model
Describes population growth in an
idealized, unlimited environment.
Unlimited growth is unsustainable because resources are depleted as population gets larger.
Equation of exponential growth:
dN/dt= rN
r-
intrinsic rate of increase
- per capita rate which population changes in size for specific time period.
Exponential population growth results in a J-shaped curve when population size is plotted over time.
Exponential growth has a constant per capita rate of increase.
Characteristic of populations introduced to a new environment OR after drastic reduction (by catastrophic event.)
Change in Population Size
Change is population size during a
fixed times interval
can be defined as:
Change in population size= Births + Immigration - Deaths - Emigration
:small_red_triangle:N/ :small_red_triangle:t = B - D
:small_red_triangle:N- change in population size
:small_red_triangle:t- time ineterval
B- # of births
D- # of deaths
Also written as:
:small_red_triangle:N/ :small_red_triangle:t = R
R- difference between # of births and # of deaths
Logistic Growth Model
Exponential growth assumes resources are unlimited and represents a perfect scenario.
Realistic models of population growth factor in
carrying capacity (K)
- maximum population size that a particular environment can sustain.
Carrying capacity is not constant and varies from population to population.
Crowding and resource limitation
affect per capita birth and death rates- causes per capita rate of population growth (r) to drop.
-Drop when cannot obtain sufficient resources to reproduce.
-Increase if starvation or disease increases density.
Produces a sigmoid (S-shaped) curve.
Logistic Population Growth
Logistic population growth
- per capita rate of population growth approaches zero when nearing carrying capacity (K).
dN/dt= rN(K-N)/K
N is small to K= (K-N) close to 1
N is large and limited resources= (K-N) close to 0.
When N=K, population stops growing.
Conservation
Conservation biologists use logistic growth model to:
-Predict rate of recovery for small populations.
-Estimate sustainable harvest rates for wildlife.
-Estimate critical point in which populations become at risk for extinction.
White rhinoceros are at risk for extinction
Life History
Life history
- comprises traits that affect reproduction and survival schedule.
Traits that are products of natural selection.
-Development, physiology, and behavior of organism.
An organism's life history entails three key factors:
Age at first reproduction (maturity)
How often organism reproduces
How many offspring are produced per reproductive episode
All three taken into account when determining the R or K strategists.
Age of Reproduction
Varies considerably across species.
Ex. loggerhead turtle reach maturity about 30 yr. old, but salmon reproduce at 3-4 yr. old.
Reproductive Rate
Vary in how often they reproduce.
Semelparity
- individuals undergo a "one-shot" pattern of big-bang reproduction.
Iteropathy
- individuals undergo repeated reproductive events throughout their lifetime.
Ex. humans
Number of Offspring
Varies
Species that produce one or few offspring typically raise their young better than those that produce many.
Trade-offs
The uses of resources for reproduction can reduce the resources available for survival and vice versa.
Species whose young have low chance of survival produce many offspring.
Ex. Dandelions.
Fewer offspring often invest more energy in each offspring to increase survival.
Ex. Brazilian nut tree
Life history variation can be related to the logistic growth model
K-selection
- selection for life history traits that are advantageous when:
-Density is high (near K)
-Resources are low
-Competition is strong
r-selection
- selection for life history traits that maximize reproductive success when
-Density is low
-Little competition for resources
Regulation of Population Growth
Population Change and Population Density
A population will:
-Grow when birth rate exceeds the death rate.
-Decline when the death rate exceeds the birth rate.
Density Independent
Density independent
- when the birth rate or death rate does not change with the population.
does NOT influence population size.
Density Dependent
Density dependent
- when the death rate increases or a birth rate decreases with increasing density.
influences population size.
one or more density-dependent factors cause it to decease when large (or increase when small).
Mechanisms of Density Dependent Regulation
Predation
Competition for resources
Disease
Intrinsic factors
Territoriality
Toxic wastes
Competition for Resources
Increasing population density in crowded populations intensifies competition for resources and reduces birth rates.
Ex. Farmers add fertilizers to reduce nutrient competition for crops.
Disease
Disease transmission rate increases as population becomes more crowded.
Ex. Flu affects density populated areas more than rural.
Territoriality
Limits population density when space is limited and becomes resource.
Ex. cheetahs use chemicals in urine to mark territory.
Intrinsic factors
Factors affect organism individually.
Ex. Brith rates drop when food and shelter are abundant.
Toxic Waste
Accumulation of toxic waste in high density areas regulate population size.
Ex. ethanol produced by brewer's yeast becomes toxic at high population density.
Population Dynamics
Population dynamics
- study that focuses on the complex interactions between abiotic and biotic factors that cause variation in population size.
Populations of large mammals can fluctuate substantially.
Boom and bust cycles: lynx and hares follow a 10-year population cycle
Immigration, Emigration, & Metapopulations
In addition to births and deaths, immigration and emigration also influence populations.
When population becomes crowded and resource competition increases- emigration increases.
Metapopulations
- groups of local populations linked by immigration and emigration.
Occupy discrete patches of suitable habitat surrounded by unsuitable habitat.
Local populations lost through extinction can recolonize by immigration from other patches.
Ex. Butterfly shift's location of occupied and unoccupied pacthes.
Human Population
Human population has grown at an unprecedented rate
Regional Patterns of Population Change
To maintain population stability, a regional human population can exist in one of two ways:
-Zero populations growth= high birth rate - high death rate
-Zero population growth= low birth rate - low death rate
Demographic transition
- move from the first to the second.
-Quality of healthcare and improved access to education.
Age Structure
Age structure
- relative number of individuals of each age in a population.
Important factor affecting population growth.
Pyramids of age structure help predict a populations growth trend.
Global Carrying Capacity
Estimated from < 1 billion to > 1 trillion
Ecological footprint
- concept that summarizes the aggregate land and water area needed to sustain a person, city, or nation.
Add all productive land and divide by # of people.
-Or calculate based on energy use
Ch. 54: Community Ecology
Terms to Know
Community
- multiple populations of different species living and interacting in the same area.
Community Ecology
- study of interactions between members and structure of a community.
Community Structure
- diversity, abundance, and organization of different species in a community.
Community Interactions
Community Interaction
- relationship between >2 organisms in a community.
Can be:
-
Intraspecific
- occurs between organisms of same species. (TRApped within species).
-
Interspecific
- occurs between organisms of different species.
Community interactions can have a positive, negative, or neutral effect on an organism's fitness.
These effects can change over time.
Interspecific Interactions
Interspecific interactions include:
Competition (-/-)
Exploitation/Consumption (+/-)
-Predation
-Herbivory
-Parasitism
Positive interactions
-
-Mutualism (+/+)
-Commensalism (+/0)
Competition
(-/-)
Competition
- >2 organisms compete
directly
or
indirectly
for the same limited, vital resource.
Competition for resources between members of the same species is called
intraspecific competition.
Impact on an organism can be:
-
Symmetric
- equal with no clear winner.
-
Asymmetric
- unequal with obvious winner.
Competing for a resource always
lowers
fitness because one loses access to resource and the other spends energy/time to obtain resource.
Competitive Situation is:
-
Direct
- competitor actively interferes with opponent's chances of success.
Ex. Face to face confrontation (fighting).
-
Indirect
- indirectly and passively decreases its opponent.
Ex. Depleting shared resources
Ecological Niche
Competition for limited resources can cause evolutionary change in populations.
Principle of Competitive Exclusion
- slight reproductive advantage will eventually lead to local elimination of the inferior competitor.
Ecological niche
- specific set of biotic and biotic resources that an organism uses in its environment.
Ex. Tropical tree lizard- temp. range it tolerates, size of branches it perches, time of day its active, sizes and kinds of insects it eats.
Two species cannot coexist permanently in a community if their niches are identical.
However, evolution by natural selection can result in one of the species using a different set of resources or similar resources at different times.
Resource partitioning
- the differentiation of niches that enables similar species to coexist in a community.
As a result of competition, species
fundamental niche (niche potentially occupied)
is different from its *realized niche (portion of fundamental niche actually occupied).
Character Displacement
Long-term outcome of resource partitioning is character displacement.
Character displacement
- the evolution of "new" traits between competing species to reduce competition.
Allopatric populations (geographically separate) are similar and use similar resources.
Sympatric populations
(geographically overlapping) show difference in body structure and the resources they use to lower competition.
Ex. Finches in sympatric populations have diverged to have different sized beaks to eat different sized seeds.
Exploitation (+/-)
Exploitation
- one organisms benefit at the expense of the other organism being harmed.
Three forms:
Predation
Herbivory
Parasitism
Predation
Predation
- when one organism, the predator, kills another organism, the prey.
Predators and prey tend to be refined through natural selection.
Predators and prey in a community are in a constant coevolutionary ams race.
Coevolution
- >2 interacting species constantly evolving in response to each other.
Predator & Prey Adaptations
Defensive Adaptations of Prey
Behavioral adaptations
- running, hiding, group living
Mechanical defenses- porcupine
Chemical defenses- skunk
Aposematic coloration
- poison dart frog (warning color)
Cryptic coloration
- camouflage
Batesian mimicry
- harmless species looks like harmful one
Mullerian mimicry
- two unpalatable species resemble each other.
Defensive Adaptations of Predator
Echo location
Sharp teeth, fangs, claws
Night vision
Venom
Heat sensing
Speed
Herbivory
Herbivory
- a herbivore consumes plants, algae, or photosynthetic bacteria.
Prey Adaptations
Physical defenses- thorns, spikes
Chemical defenses- toxins.
Herbivore Adaptations
Specialized stomach for digesting plants
Teeth/mouth adapted to consume and chew
Parasitism
Parasite
- organism that lives in or on another organism (host), gaining resources from it.
Ectoparasite
- lives ON host (not fatal)
Ex. Tick/lice
Endoparasite
- lives IN host (not fatal)
Ex. Tapeworm
Parasitoid
- lays larvae on/in host; larvae feed on host when they hatch and usually
kills
the host.
Ex. Wasps
Positive Interactions
Positive interaction
- one individual benefits and the other either benefits or is not harmed.
Mutualism
Commensalism
Mutualism (+/+)
- both organisms benefit.
Obligate mutualism
- two organisms depend on each other for their survival.
Ex. Oxpecker eats tick from Impala's fur--> fur gets clean and tick removed.
Commensalism (+/0)
- one organism benefits, the other is NOT affected.
Community Structure
Community structure
- the make-up of a community
-Has four key attributes:
Species richness
Relative abundance
All of the interactions between organisms
Physical attributes- biotic and abiotic including species distribution.
Species Diversity
Species Diversity
- variety of different kinds of organisms that make up a community.
Two components:
Species richness
- total # of different species.
Relative abundance
- proportion of each species in relation to ALL individuals in the community.
Shannon diversity index (H)
- index that calculates diveristy based on species richness and relative abundance.
H = - (pA ln pA + pB ln pB + pC ln pC + ...)
ABC- species in community
p- relative abundance of each species
ln- natural logarithm
Diversity and Stability
Higher diversity communities are more productive and better able to withstand or recover from environmental stresses.
Diverse communities are more stable year to year in productivity of
biomass
- total mass of all organisms in a habitat.
More resistant to
introduced species
- organisms humans have moved to regions that are not native.
Trophic Structure
Trophic structure
- feeding relationships between organisms in a community. Who eats who?
Food chain
- linear sequence of organisms where each is eaten by the next. Transfer of chemical energy from each level to the next.
Food web
- complex network if interconnected food chains in a community.
Trophic level
- position an organism occupies in a food chain/web.
Primary producer
Primary consumer
Secondary consumer
Tertiary consumer
Quaternary consumer
Food Chain
Food Web
Limits on Food Chain
Energetic hypothesis
- length of food chain is limited by the inefficiency of energy transfer along the chain.
~10% of the energy stored in organic matter at each trophic level in converted to organic matter at the next trophic level.
Species Impact on Community Structure
Certain species have a significant impact on community structure through trophic interaction and their influence on physical environment.
Foundation species
Keystone species
Ecosystem engineer
Foundation Species
- have strong community-wide effects (provides habitat/food) due to its large biomass.
Ex. Trees, shrubs, algae
Abundant and if removed have big impact on other trophic levels.
Can be competitively dominant- superior exploiting key resources like space, water, nutrients or light.
Keystone Species
- small biomass but plays large ecological role that's disproportionate to its abundance.
Ex. Sea star
Ecosystem Engineer
- influence a community significantly by altering its physical environment.
Ex. Trees can also be considered ecosystem engineers because their presence modifies the physical environment that create habitats that other species depend.
Ex. Beavers
Bottom-Up & Top-Down Controls
Some population sizes cycle due to interspecific interaction. Cycling can be explained from up or down.
Ways in which adjacent trophic levels affect one another can occur in two general ways.
Bottom-up control
- what they eat
Top-down control
- what eats them.
Bottom-Up Control
- cycles influences by resource or food availability. (producers)
Limited by nutrient supply or availability of food at lower trophic levels.
To change the community structure, biomass at lower trophic levels needs to be altered.
Ex. add nutrients to stimulate plan growth, each trophic level higher will increase in biomass.
Top-Down Control
- cycles influenced by organisms at higher trophic levels. (predators)
Predators limit lower trophic levels.
Applied to improve water quality in lakes with high abundance of algae.
Community Dynamics
Disturbances influence species diversity and composition.
Disturbance
- an event that significantly changes/disrupts a community.
Impact level depends on disturbances:
-Type
-Frequency
-Intensity
Nonequilibrium model
- model describes most communities as constantly changing after disturbance.
Intermediate Disturbance Hypothesis
- moderate levels of disturbance foster the MOST species diversity.
High levels of disturbances prevents many species from establishing and surviving.
Best competitors dominant in lower levels of disturbances.
Ecological Succession
Ecological succession
- gradual process by which a community's structure changes over time.
Each existing community alters its environment, allowing new species to thrive.
Occurs at all times in all communities, but disturbances accelerate the process.
Three type of Ecological Succession:
Primary succession
Secondary succession
Climax community
Human disturbances are some of the strongest disturbances.
Primary Succession
- when organisms colonize a currently uninhabitable area with NO soil.
Process begins in a virtually lifeless area.
Most life-forms initially present are prokaryotes and protists.
Pioneer species
- first species to colonize during primary succession (help from soil).
Secondary Succession
- when a community recovers after a disturbance that leaves the soil intact.
Not all organisms had been removed.
Can return to something like its original state.
Climax Community
- the "final", most stable stage of ecological succession.
Early-Arriving Species VS. Late-Arriving Species
In ecological succession, three way early-arriving species can affect late-arriving species:
Facilitation
- early-arriving species makes conditions MORE favorable for certain later species.
Tolerance
- existing species do NOT affect the arrival of certain later species.
Inhibition
- presence of a certain species inhibits establishment or regrowth of another.
Geographic Impact on Communities
Large-scale biogeographical factors contribute to range of diversity in communities.
Two biogeographical factors have significant impact on a community's diversity:
Latitude
Area
Latitude
- diversity typically decreases with increasing latitude further from the equator.
Two factors affect latitudinal specie richness:
Evolutionary history- tropical communities tend to be older (more time for speciation/evolution).
Climate- near equator fosters more productivity (sunlight and precipitation).
-
Evapotranspiration
- evaporation of water from soil and plants.
Area
- diversity typically increases with increasing area (larger areas have more resources).
Species-area curve
- all other factors being equal, larger geographical area of community the more species it has.
Island Equilibrium Model
Island equilibrium model
- # of species on an "island" eventually reaches equilibrium (immigration=emigration).
Island= oceanic islands, lakes, mountain peaks, and patch.
The # of species at this equilibrium depends on two factors:
-
Size
- the larger the islands area = more species present at equilibrium.
-
Distance
- the closer to the mainland = more species present at equilibrium.
Pathogens
Pathogens alter community structure locally and globally.
Pathogen
- disease cause microorganism.
Effects on Community Structure
Affect coral reef communities and terrestrial ecosystems.
Zoonotic Disease
Zoonotic pathogens
- transferred to humans by other animals through direct contact or
vector
- intermediate species.
-Vectors- parasites, ticks, lice, mosquitos.
Climate change and destruction of natural habitats increase the risk of coonotic diseass.
