Populations can be described by Distribution Numbers Age structure Density

Populations cannot grow indefinitely (r) because there are limited by resources and habitats (k= carrying capacity).

ClumpingUniform dispersionRandom dispersion

i.e., Plethodon sp. salamanders are found clumped under fallen logs in the forest

the night lizard Xantusia sp. is found clumped within fallen Joshua trees in the Mojave desert

Plants often clump because their seeds fall close to the parent plant or because their seeds only germinate in certain environments. Impatiens capensis is an example.

This generally happens because of interactions between individuals in the population.

Competition: Creosote bushes in the Mojave desert are uniformly distributed because competition for water among the root systems of different plants keep them separated.

Territoriality: The desert lizard Uta sp. maintains somewhat regular distribution via fighting and territorial behavior

Human Intervention: I.e., the spacing of crops.

This pattern occurs in the absence of strong attraction or repulsion among individuals. It is uncommon. For example, fig trees in the amazon

rain forest. This random distribution might be due to seed dispersal by bats.

Simply the number of individuals in the population at any given time. Sometimes called abundance.

This is the relative number of individuals at different ages.

Broken down by: Prereproductive age Reproductive age Postreproductive age

Which population structure would lead to stable growth?

Which leads to an increase in population? Decrease?

Which types of countries do you think follow a stable growth? Increasing? Decreasing?

The number of individuals in the population per unit area or unit volume. For many organisms, it is the density of

a population rather than its actual numbers, that exerts a real effect on the organism.

There are 10,400 mice living in a 1000m x 1000m field. What is the density of this population?

The area of the field is 1,000,000 square meters (m2).

The density of mice is therefore 10,400 mice/1,000,000m2=.0104/m2.

Birth (Natality)Death (Mortality) ImmigrationEmigrationPopulation change= (B+I) –

(D+E)

This is probably the best, simple, model of population growth…it predicts the rate of growth, or decay, of any population where the per capita rates of growth and death are constant over time. In exponential growth models, births,

deaths, emigration and immigration take place continuously.

What must exist for populations to grow in this way?

Density independent

Results from sudden crash in population size

Outstrip resource limit

catastrophe

Populations tend to grow to the maximum extent possible given environmental conditions

Intrinsic rate of increase (r)= rate of population growth if unlimited resources available

Also called biotic potential

Biotic potential cannot be sustained

Environmental resistanceNegative feedback▪Snowshoe hare and lynx

Populations grow until one or several limiting resources become rare enough to inhibit reproduction so that the population no longer grows.

Eventually, every population reaches its carrying capacity, this is the maximum number of individuals a given environment can sustain.

Density dependent

Recycling and renewal of resources

Establishes equilibrium around carrying capacity

A: lag phaseB: acceleration

phaseC: exponential

growthD: deceleration

phaseE: equilibriumG: dynamic

fluctuations

Adaptive traitsTechnological advancesHow have we changed the carrying

capacity for human population growth to continue?

Density- dependent factors Intraspecific competition Predation Disease

Density-independent factors Natural disasters Pollution Habitat destruction (deforestation)

What is an example of a density dependent and independent factor?

Examples: For Neodiprion sawflies, winter surviorship is greatly affected by the weather, which is density-independent. During the summer, however, parasitic wasps

impose very high density-dependent mortality. Pacific mussels, Mytillus sp., are largely

limited by density-dependent competition for space on rocky outcrops. Occasionally, density -independent disturbance by floating logs decimates populations.

Stable Rainforest species

Irruptive Insects

Cyclic- (boom and bust) Lemmings▪ http://www.youtube.com/watch?v=pDqlZjpSJCc

Wolf-moose interactions Irregular

Due to catastropies

Why are deer referred to as an “edge species”?

What are controls to deer population?

What is the deer dilemma?

Delayed density dependence

SEXUAL What are pros and

cons to this type of reproduction?

ASEXUAL What are pros and

cons to this type of reproduction?

r-selected Reproduce early and

put most of their energy into reproduction

Many small offspring High growth rate

Population size fluctuates wildly around carrying capacity

Low ability to compete Most offspring die

before reaching reproductive age

K-selected Fewer, larger

offspring High parental care Most offspring survive

to reach reproductive age

Lower growth rate High ability to

compete Population size fairly

stable around carrying capacity

Positive: enhance population growth

Negative: reduce population growth

PredatorsDiseasesPheromones

Type I (Late Loss): large animals immune to predation, live to old age

Type II (Constant Loss): mostly prey, predation is constant throughout lifespan

Type III (Early Loss): large numbers of young because most will be eaten, only few adults survive