Population Ecology

Presented by: Czaresse, Gem, Kazzandra, Kendall, Lauryn, and Melissa

You Must Know➢ How biotic and abiotic factors affect the distribution of biomes.➢ How density,dispersion, and demographics can describe a population.➢ The differences between exponential and logistic models of population growth➢ How to apply mathematical models to predict changes in population growth

rates or size➢ How density-dependent and density-independent factors can control

population growth➢ Interactions between populations affect the distributions and abundance of

populations ➢ How a change in matter or energy will affect the population or community➢ The effect of age distributions and fecundity on human populations as

presented in age- structure Pyramids

40.1 Earth's ClimateHow does the earth’s climate influences the

distribution of terrestrial biomes?✢ 4 Physical Factors: Temperature, Precipitation,

Sunlight, and Wind

Global Climate Patterns✢ Determined by the input of solar energy and Earth’s

movement in space

○ Latitudinal Variation in Sunlight Intensity

○ Global Air Circulation and Precipitation Patterns

✢ The sun warms the atmosphere, land, and water

○ Temperature variation, movement

of air and water, and evaporation; causing

latitudinal variations in climate

Regional Effects on the Climate Climate varies seasonally and can be modified by...

✢ Seasonality: Earth’s tilted axis of rotation and its annual

passage around the sun cause a strong seasonal cycle

✢ The changing angle of the sun affects

local environments

✢ Seasonal changes in wind patterns,

alter ocean currents

Bodies of Water ✢ Oceans current influences the climate along the coasts of

continents by heating or cooling air mass

✢ High specific heat of water, ocean and large lakes tend to

moderate the climate

nearby land

Mountains ✢ Mountains influence air flow over land When land is warmer

than the water, air over the land heats up drawing cool breeze

from the water to the land

✢ Mountains also affect the amount of sunlight reaching an area

and thus the local temperature and rainfall

Climate and Terrestrial Biomes ✢ Location of

terrestrial biomes shows latitudinal patterns

✢ 30 north and south leads to formation of deserts

Climograph✢ climate on the distribution

of biomes

✢ annual mean temperature

and precipitation in a

particular region

✢ North America with a

particular combination of

temperature and

precipitation

Terrestrial Biomes✢ Terrestrial biomes are names for major physical or climatic

features, and their predominant vegetation

✢ Vertical Layering of vegetation is an important feature of

terrestrial biomes

○ Top canopy, low-tree layer, shrub, ground layer

✢ Non forest biomes similar, less pronounced, layers

○ Provides many different habitats for animals

Savanna

Distribution: Equatorial and subequatorial regionsClimate: Temperature Avg. 25-29C Tropical rainforest: constant rainfall 200-400 cmTropical dry forest: Avg. Precipitation 150-200cm

Distribution: Equatorial and subequatorial regionsClimate: temperature avg. 24-29CRainfall avg. 30-50cmHuman Impact: Fires, cattle ranching, and over hunting

Tropical Forest

Desert Chaparral

Distribution: Desert 30 north and south latitudeClimate: temperature exceed 50 C in hot deserts, fall below 30 C in cold desertsHuman Impact: urbanization and conversion

Distribution: Midlatitude coastal regions Climate: precipitation 30-50 cmFall, winter, spring- 10-12CSummer 30CHuman Impact: Fires, cattle ranching, and over hunting

Temperate Grassland

Northern Coniferous Forest

Distribution: Typically at midlatitudesClimate: precipitation avg. 30 to 100 cmAvg. temperature below -10C winter, and 30C in summer Human Impact: converted to farm lands, and cattle and other grazers turned biome into desert

Distribution: largest terrestrial biomeClimate: precipitation 30 to 70 cmHuman Impact: being logged at a fast rate, and old-growth stands may soon disappear

Temperate Broadleaf Forest Tundra

Distribution: Midlatitudes in the Northern HemisphereClimate: Precipitation avg. 70 to 200 cmHuman Impact: logging and land clearing for agriculture and urban development

Distribution: Covers areas of the arctic, 20% of the earth's land surface Climate:precipitation avg. 20 to 60 cm, winter below -30 C, and summer less than 10 CHuman Impact: mineral and oil extraction

40.2 Aquatic Biomes

Aquatic biomes are primarily characterized by their

physical and chemical environment.

✢ Marine Biomes: Salt concentration average 3%

✢ Freshwater: Salt Concentration <0.1%

✢ Photic Zone: Sufficient light for photosynthesis

✢ Aphotic Zone: Little light

✢ Pelagic Zone: Combination of photic and aphotic zones

✢ Benthic Zone: Bottom of these zones

○ Occupied by organism communities called benthos

✢ Littoral Zone: Close to the shore; shallow enough for

rooted plants

✢ Limnetic Zone: Waters far from the shore

Zonation

Zonation in a Lake

Exploring Aquatic Biomes

Wetlands & Estuaries Lakes

Wetlands: Sometimes inundated with water

and supports plants for water-saturated soil.

Estuary: Transition zone between river and sea.

Standing bodies of water ranging from ponds

that are a few square meters to thousands of

square kilometers.

Exploring Aquatic Biomes (cont’d)

Streams & Rivers Intertidal Zones

Headwater streams: Cold, clear, turbulent,

swift.

Downstream: Warmer, more turbid.

Area on most marine shores that is periodically

submerged and exposed by the tides twice a

day.

Exploring Aquatic Biomes (cont’d)

Coral Reefs Oceanic Pelagic Zone

Formed from the calcium carbonate skeletons

of corals. Require high oxygen levels and very

sensitive.

The open ocean. Surface is constantly mixed by

wind-driven currents. 70% of the Earth’s

surface.

Exploring Aquatic Biomes (cont’d)Marine Benthic Zone

The seafloor. The marine benthic zone is dark

except for shallow, near-coastal areas.

40.3 Distribution of SpeciesWhat factors determine the distribution of species?

✢ Dispersal: the movement of individuals from their area

of origin or from centers of high population

○ e.g. birds

✢ Biotic: other living species

✢ Abiotic: temperature, water, oxygen, salinity, or soil

Biotic Factors✢ Predation

○ organisms kill their prey

✢ Herbivory

○ e.g. sea urchins can limit the distribution of

seaweed

✢ Presence/absence of: pollinators, food, parasites, and

pathogens

Abiotic Factors✢ Temperature: most organisms function best within a

specific temp. range

✢ Water and Oxygen: species can be at risk of drying out

○ water can affect oxygen availability in aquatic

environments

○ oxygen concentration can be particularly low in

both deep ocean and lake waters

✢ Salinity: aquatic organisms are restricted to either

freshwater or saltwater habitats due to osmoregulation

Abiotic Factors (cont’d)✢ Sunlight: provides energy that drives most

ecosystems

○ too little sunlight can limit photosynthetic species

✢ Rocks and Soil: the pH, mineral composition, and

physical structure of rocks can limit plants, thus

herbivores and omnivores are also affected

40.4 PopulationHow does biotic and abiotic factors affect population

density, dispersion, and demographics?

✢ Density: the number of individuals per unit area or

volume

✢ Dispersion: the pattern of spacing among individuals

within the boundaries of the population

✢ Demographics: the study of vital statistics of

populations and how they change over time (particularly

birth and death rates)

DensityHow is density determined?

1. counting all individuals within the boundaries2. calculate the average density in one are and then extend it

to the entire area to estimate the population sizea. individuals b. indicators (nests, burrows, tracks, fecal droppings)

How is density changed?

1. Increase: births and immigration 2. Decrease: deaths and emigration

Dispersion ✢ Clumped

✢ favorable environmental

factors

✢ mating behavior

✢ accessible food

✢ defense

✢ Uniform

✢ competition○ plants secrete

chemicals to inhibit growth and germination of others

✢ antagonistic social interactions

✢ Random

✢ absence of strong

attractions or repulsion

✢ physical or chemical

factors

○ wind blown seeds

Demographics Life Table: summary of

age-specific survival and

reproductive rates

Cohort: group of individuals of

the same age from birth until

death

✢ determine deaths and

survivals , keep track of

offsprings produced

(focused on females)

Demographics (cont’d)Reproductive Rates

✢ typically measured as

the average number of

female offsprings for

each female

✢ age-specific

reproductive rates

✢ high reproductive rates

do not lead to rapid

population growth

Survivorship Curve: plots numbers of survivors in a cohort

40.5 Population Growth

Change In Population Size:

Change in population size Births + Immigrants - Deaths - Emigrants

(Change in pop. size/ change in time)

Nt

B - D(# of births

- # of deaths)

R(difference between B

and D)

^ simplified version, ignoring immigration/emigration

Exponential Growth

per capita change in population size (r )t

dNdt

rN dN = the size of the population at a particular instant in time

dt = the time interval involved in the calculation

N = current population size

r = intrinsic rate of increase - the per capita rate at which an exponentially

growing population increases in size at each instant in time

For example: Population of 1,000 increases by 16 annuallyChange (per capita) is 16/1000, or 0.016

(r )Nt

0.016 X 1000 = 16 per year

t = the time intervalr = contribution that an average member of the population makes N = population size0.016 X 500 = 8 per year

In a population of 750 fish, 25 die on a particular day while 12 were born. What is the per capita rate of increase for the day?

Example problem

In a population of 750 fish, 25 die on a particular day while 12 were born. What is the per capita rate of increase for the day?

25-12 = 13 on the day

Change per capita is 13/750 = 0.0173

Example problem

Logistic Growth

Carrying capacity (K): the maximum population size that a particular environment can sustain

dt

dNrN

(K-N)

K

K - N = the # of additional individuals the environment can support(K-N)/K = the fraction of K that is still available for population growthWhen N < K, (K-N)/K is close to 1; per capita rate is largerWhen N > K, (K-N)/K is close to 0; per capita rate is smaller

Population size (N): 50

Births: 10

Deaths: 4

Carrying capacity: 400

Find population logistic growth rate.

First, find r.

rN (K-N)

K

Example problem

Population size (N): 50

Births: 10

Deaths: 4

Carrying capacity: 400

Find population logistic growth rate.

First, find r (individual growth rate).

rN (K-N)

K

Example problem

10-4=66/50 = 0.12 = r

(0.12)(50)(400-50)

400= 5.25

40.6 Population Dynamics

How does life history and population density influence population dynamics?

✢ Population dynamics

○ fluctuations in population sizes

○ interactions between biotic and abiotic factors

that cause variation in population size

Life History & Trade offs

✢ Life history- Traits that are evolutionary

outcomes that affect an organism’s schedule of

reproduction and survival

✢ Selective Pressure

○ Influence trade-offs between number and

size of offspring

○ More likely to die= more offspring

Density Dependent* A death rate that increases with population density

or a birth rate that decreases with rising density

✢ K-Selection

○ Selection for traits that are sensitive to population

density and favored at high densities

○ Parental care

○ Long life expectancy

○ Ex: Humans, Trees

Density Independent

* A birth rate or death rate that does not change with population density

✢ R-Selection

○ Selection for traits that maximize reproductive success

in low density environments (uncrowded)

○ Many offspring

○ Disturbed habitats (Ex: Freshly Burned Grassland)

Population Regulation

✢ Negative Feedback○ Density Dependant regulation○ Stops population growth (reducing birth

rates/increasing death rates)○ Ex. Toxic waste, Territoriality, Disease,

Competition for resources✢ Metapopulation helps ecologists understand

population dynamics and gene flow in patchy habitats

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