BIOS104 Population Biology

What is a population?

The total hunger of individuals of a single species in one place

What is population biology?

study of population size

what is population dynamics?

study of variation in population size over time

How do we measure population size?

Absolute and relative size

what is absolute population size?

estimating the total number of individuals in a region

what is relative population size?

estimating trends in numbers without ascertaining the total

how can we measure absolute population size?

mapping nets, drone, satellite images

how can we measure relative population size?

standardized walks/observations

collection in traps

camera trap records

citizens

what does a realistic model to study changes in population size include?

immigration and emigration

understand sources of mortality

is the initial growth of an organism in an environment exponential?

yes

what does r signify in the exponential growth equation?

intrinsic rate of natural increase

what does the intrinsic rate of natural increase mean?

maximal growth rate per individual when species is rare and resources superabundant

do fast reproducers have a high or low r?

high → strong growth from rare

do slow reproducers have a high or low r?

low → slow growth from rare

what does sigmoidal population growth mean?

after time, growth slows → sigmoid curve

What does K signify?

carrying capacity → number of individuals the population settles at

what does N>K mean?

shrinking population

what does N=K mean?

stable population

what does N<K mean?

growing population

why does growth stall as population size increases?

density dependent effects

• mortality increases with density

• fecundity decreases with density

• dispersal increases with density

What else can cause changes to population size?

environmental effects

what is a maximum sustainable yield?

point where population growth is maximised → K/2

B-D

What are the 2 types of intraspecific competition?

Exploitation and Interference

What is exploitation competition?

no direct interaction, competition through shared resource

What is interference competition?

prevent access of others to resource to acquire exclusive access

What happens under exploitation competition?

individuals distribute to follow resource distribution

How can organisms ‘reserve space’?

microbes - toxins in surrounding that they are immune to

allelopathy in plants → seed coat on plants secrete toxins into soil around them so nothing else can grow

do species with exploitation competition have more or less stable population size?

less stable

Why are big fierce animals rare?

• larger than prey

• low ecological efficiency→ energy (respiration), active capture (failed)

What are consequences of small populations?

• inbreeding depression

• build up of lethal recessive alleles → infertile or inviable

• lack of variation for adaption

why is demographic instability an issue for megafauna?

they have low r as they build back slowly → energy into defence and mating

repeated events → extinction

What are allee effects?

small populations fail because they start to lose their social interactions

What does demographic instability and allee effects mean for small, rare populations such as big, fierce animals?

population decline may accelerate at small population size

→ social species, species with poor mate finding

What did Ehrlich estimate the optimal human population size to be?

2 billion

Why did Simon say human populations could increase indefinetly?

resource scarcity drives price rises

→ price rises incentivise efficiency gains (human ingenuity)

→ resources are infinite in economic terms

What are Cohen’s solutions to population?

• new technology to enlarge capacity

• stop population growth and reduce consumption

• eliminate corruption, violence and inequalities between rich and poor