Lecture 11 Populations

Question 1

Population

Answer 1

A group of interbreeding individuals found within a given area at a given time

Question 2

Individual: unitary species

Answer 2

Zygote formed through sexual reproduction grows in to a genetically unique organism e.g. fish, humans and many insects known as ‘genets’

Question 3

modular species

Answer 3

Asexual/vegetative reproduction

Zygote develops into a module that asexually produces further similar modules - a ‘genet’ produces a ‘ramet’ e.g. some plants, sponges, bryozoans and corals

Question 4

Largest organism in the world

Answer 4

Aspen grove in Utah covering 0.43km squared each stem could be considered a ramet and therefore individual for purpose of defining a population

Question 5

Describe a population : spacial distribution

Answer 5

Spacial distribution - location of individuals within a population stationary (sessile) vary (migratory)
Mixing through flow of individuals/gene flow may be uniform - equally distributed or random or aggregated (clumped in groups)

Question 6

Describe a population: gene flow

Answer 6

Less frequent movement of individuals or reproduction between parts of a population defines local or sub-populations

Question 7

Describe a population: metapopulations

Answer 7

Linked throughout/across landscape by immi/emmigration

Question 8

Population density

Answer 8

No. Of individuals in area covered

Question 9

Population structure

Answer 9

Not all individuals the same, vary in: spacial location/origin, age,sex or size

Can categorise individuals by age and no. In each category (age structured pop.) E.g. 0-1, 1-2, 2-3 etc.

Often more logical to categorise according to stage of development (stage structured pop.) Categories: juvenile, sub adult, adult or pre reproductive, reproductive, post reproductive

Question 10

Life tables

Answer 10

Used to understand pop. Struct change over time

2 approaches
1) snapshot of info about individuals of diff ages at one time
2) follow survivorship of a cohort of individuals over time

E.g. Acorn barnacle native to Pacific, now invading intertidal zones in Europe and Argentina (adults sessile larvae free living plankton)

Question 11

Survivorship/fecundity

Answer 11

Survivorship - no. of individuals surviving to an age out of total

Fecundity - no. of offspring per surviving individual of certain age

Question 12

Survivorship curves

Answer 12

Plot survivorship over time to produce survivorship curve X axis age and y acid no. of survivors (log scale)

eg. Acorn barnacle have high no. Larvae, most die, those that survive settle on rocks and become sessile adults with high survivorship

Other species have high survivorship at early ages e.g. mountain sheep and humans

A third type of curve represents constant survivorship

Question 13

Life history strategies

Answer 13

the way individuals within/among species allocate resources to growth, repro, and survival based on genetic and enviro factors

Limited resources result in tradeoffs

Can be r selected - usually pest/weed species : high ability to reproduce i.e. high fertility rate, small body size, early onset of maturity, short time of generation, and the capability to disperse off the progeny widely. Often reproduce once a large quantity of offspring. Periods of exponential growth followed by periodic/seasonal decline. Tolerate unpredictable conditions

Or k selected - reproductive strategies tend towards heavy investment in each offspring, are more common in long-lived organisms, with a longer period of maturation to adulthood, heavy parental care and nurturing, often a period of teaching the young, and with fierce protection of the babies by the parents. Reproduce more than once producing few offspring. Slowly rising pop that stabilises at carrying capacity. thrive in stable enviro e.g. humans

Question 14

Population dynamics

Answer 14

Births & deaths, immigration and emmigration affect pop. dynamics

Pop change :

Nt+1 = Nt+Bt-Dt+It- Et
No. of individuals in pop at time t+1=
(Nt) No. If individuals at t +
(Bt) no. Of births between t and t+1 -
(Dt) no. Of deaths between t and t+1 +
(It) no. Of immigrants between t and t+1-
(Et) no. Of emigrants

In a closed pop I=E=0 - no individuals leave or arrive

Question 15

Why use pop. Dynamics?

Answer 15

To manage and conserve species, understand birth/death rate find out risk of extinction and estimate sustainable harvest rates e.g. timber trees and fishing

Question 16

Modelling pop change

Answer 16

In closed system Delta N = B-D
Express B & D as per capita rates for pop ( N) at time (0)

B= bN0 = birth per capita
D= dN0 = death per capita

So B-D is the diff between birth and death rate aka the per capita birth rate (r)

Question 17

Population growth rate

Answer 17

Change in pop written as

Delta N = rN0

When b>d r>0 pop increase
b<d r<0 pop decrease
b=d r=0 pop no change

r= per capita birth rate

Question 18

Modelling populations: exponential growth model

Answer 18

All pop. Have potential for exponential growth if resources unlimited, no migration and no mortality

N(t) =N(0)e^rt

(r - per capita growth rate doesn’t change)

If r=0.5 in year 1 (t=1) then N1 will be 100xe^(1x0.5) = 1.65

Question 19

Modelling populations: logistics growth

Answer 19

Most pop do not grow indefinitely growth slows until b~d and per capita growth rate r~0

dN/dt= r max (k-N/k)N
or dN/dt=r max(1-N/k)N

k= carrying capacity: no. Of individuals that any particular environment can sustain indefinitely

r max = pop growth rate when pop v. Small

Growth is fastest when pop size is k/2 (r is highest)

E.g. k=100 N=99 r max = 1

dN/dt= 1(1/100)99= 0.99
So r*99=0.99
r= 0.01 positive growth

Question 20

Factors limiting population growth

Answer 20

K - carrying capacity, can be determined by density dependent factors

Limiting resources

Intraspecific competition e.g. for food

Predators may be attracted to prey dense areas so death rate rises

Pathogens - may spread more easily in dense pop leading to rise in death rate

Question 21

Population summary

Answer 21

Can be defined by spatial distribution, no. And density of individuals and age structure

Life tables summarise demographic changes and survivorship over time

Survivorship curves link to life history strategies

Pop dynamics can be modelled w/exponential and logistic growth models (latter accounts for carrying capacity k)

Can be impacted by density dependent/independent factors