Topic 8

Whats population size

number of individuals alive at a particullar time in a particular place influenced by births, deaths

Population growth is

study of change in total numbers of individuals in a population , change from one generation to the next

equation for calculating total change in population numbers general

births-deaths= Nt+1 - Nt

whats per capita (individual) birth rate and death rate and calculated by

the average number of births per individual in a population over a specific time period. b or d = BorD/Nt where BorD is the total number of births or deaths during that period and Nt is the total population size at the beginning of the period.

What is per capita growth rate ( r) used for

predicting population size changes r= b-d

r> 0 growing

r< 0 shrinking

r= 0 no change

How can you calculate the population size change between points

Nt+1= (1+r)Nt0

in order to calculate this for more generations, for each generation add another (1+r)

Whats the exponental growth function

growth prediction under ideal conditions

• growth rate will always be at a maximum, no limitations rmax

• rmax is always constant and positive

• rmax can vary by species but stays the same once defined

How does rmax vary by species

Hypometrically, larger organisms have slower growth rates while smaller organisms tend to have faster growth rates. This is due to differences in reproductive strategies, metabolism, and life cycle lengths.

In real life conditions

• r is not constant

• there are limitations due to disease predation etc

• growth rate r tends to decline but depend on changing births and deaths

whats carrying capacity

point at which the births and deaths are equal when r=0

represented by K

What model predicts population growth rate with predicted effects of N on r

logistic model, based on changing growth rate as populations reach carrying capacity K

assumes r decreases as population increases

On a log model for population growth when

r> 0, r<0 and r=0 in per capita population growth

r>0 Population #(N) < K (carrying capacity), growth occurs. r<0 Population #(N) > K, decline occurs. r=0 Population #(N) = K, stable equilibrium.

Population size through time relationship

r decreases as N increases , populations grow so deaths increase and births decreaseuntil carrying capacity (K) is reached, leading to stabilizing effects on population size.

r(rate at any given time)= rmax(k-Nt/k)

lower r over same # generations compared to a larger r will

take longer to reach carrying capacityand may stabilize at a lower population size.

same r but with increased population size will

take less time to reach carrying capacity and stabilize at a higher population size.

higher r values will result in

overshooting and oscillating dynamics around the carrying capacity, as populations experience rapid growth followed by significant declines.

as r keeps increasing

the growth patterns will become more randomized

Density dependance

is a process where population growth rates are influenced by the population density. As density increases, factors such as resources become limited, affecting growth.

reasons for density dependance occuring

usually biotic, relating to other organisms like disease, competitions and predation

Crowding density dependent influences

reproduction, lower at higher densities due to increased competition and stress. Growth rate slower at lower mass, reduced size and shorther lifespan

Density independent factors influencing population growth

abiotic, temperature, percepitation, natural disasters and habitat destruction

How does life history drive population dynamics

high rmax= high potential to overshoot K = unstable dynamics

K selection

refers to a reproductive strategy where organisms produce fewer offspring but invest more resources in raising them, leading to greater survival rates in stable environments.

r selection

refers to a reproductive strategy where organisms produce many offspring with little or no parental care, leading to lower survival rates in unstable environments.

consistent density numbers are associated with which selection and why

K selection, because it emphasizes stable populations with fewer offspring and greater parental investment thats more stable

which selection is assosiated with fuctuating and unpredictable densities

r selection, as it focuses on high reproductive rates to compensate for higher mortality in unstable environments.

According to the logistic model of population growth, what happens to the absolute number of individuals by which a population grows during a given time period?

Question 1 options:

A)

It is highest when the per capita growth rate is greatest

B)

It remains constant as the population size increases

C)

It gets steadily larger as the population size increases

D)

It is highest when the population is at an intermediate size (when N = K/2)

D)

It is highest when the population is at an intermediate size (when N = K/2)

As the generation time of a species gets longer, the intrinsic rate of increase tends to:

decrease due to longer intervals between reproductive events.

If the per capita growth rate is a zero (0), then

the population size remains stable, showing no increase or decrease over time. births=deaths

An environment can only support a certain number of individuals from a given species at any one time. This number is referred to as the _____ of that environment

carrying capacity

Which of the following is descriptive of a population experiencing exponential population growth?

as population size increases the resources remain unlimited

You are studying a population of 906 African ground squirrels (Geosciurus inauris) growing exponentially and track the size of the population over a period of 3 years. If 55 offspring are born and 13 individuals die in the first year, then what is the population size (rounded to the nearest whole number) at the end of your study?

1038 rounded

find r first by b-d/n

then apply to formula Nt= (1+r)^t N where t is 3 yrs and N is 906

what is r max

the per capita growth rate for exponential growth under ideal circumstances with no limitations, always positive and constantIt represents the maximum potential growth rate of a population when resources are abundant.

what is r

per capita growth rate representing births minus deaths over timein a population, often expressed as a decimal. It indicates the change in population size relative to the initial population.

r max varies by species how

Scaling Hypsometrically with body size meaning larger organisms tend to have lower r max values while smaller organisms typically have higher r max values.

in real life due to limitations organisms dont live under ideal conditions meaning

that their growth rates are often lower than r max, affected by factors such as resource availability, environmental conditions, and competition.

whats a logistic population growth

A model that describes how populations grow in a restricted environment, initially increasing exponentially until resources become limited, resulting in a stabilization at carrying capacity.

What is universal about real life species growth

density dependance meaning the growth rate of a population is influenced by its density, where high population densities can lead to reduced growth rates due to resource competition and other limiting factors.

why does density dependance occur

It occurs due to limited resources, competition, and environmental pressures that affect population growth as density increases. mostly biotic reasons relating to other organisms

How is reproduction a density dependent influence

Reproduction can be density dependent as higher population densities lead to increased competition for mates, reduced availability of resources for raising offspring, and greater potential for stress-related issues, all of which can decrease reproductive rates.

how is survival influenced at high density

Survival at high density is influenced by increased competition for resources, higher susceptibility to disease, and heightened stress levels, which can all reduce the overall survival rates of individuals in a population.

how is adult size influenced at higher density

Adult size at higher density can be influenced by competition for resources such as food and space, leading to stunted growth, reduced body size, or delayed maturation.

how is growth rate influenced at high densities

Growth rate at high densities is influenced by competition for limited resources, which can result in reduced nutritional intake, lower energy availability, and ultimately slower growth rates in individuals within the population.

what are abiotic influences of population growth

abiotic influences of population growth include factors such as temperature, precipitation, light availability, and nutrient levels. These environmental conditions can directly affect the reproductive rates, survival, and distribution of populations.

whats crowding

Crowding refers to the situation in which individuals in a population are in close proximity to one another, leading to increased competition for resources and potential negative effects on growth, reproduction, and survival.

whats a r selected species concept

species aiming to maximize growth rate

• short life span and maturation

• many offspring with low parental care

• usually one reproductive event

• high mortality

• small body size

whats k selected species concept

aim to live near carrying capacity K, stable population

• slower growth rates

• longer life span and maturation

• higher parental investment

• multiple reproduuctive events

• larger body size

• lower mortality rates

whats K

carrying capacitythe maximum population size that an environment can sustain without detrimental effects.