C4.1 Populations and communities

Population

group of individuals of the same species which live in the same geographical area and can interbreed

systematic sampling

collecting samples across a transect at regular intervals

random sampling

choosing random areas reduces any bias

Estimating population size of sessile organisms

using quadrats

Capture-mark-release-recapture method

Used for motile organisms

1. Catch and mark

2. release

3. after a period of time collect again

4. use the lincoln index to estimate population size

Lincoln Index

population size = number of organisms captured inititally x number of all organisms recaptured/marked organisms recaptured

Limitations of capture-mark-release-recpature method

• assumes pop is closed no emigration or immigration

• animals can be injured by capturing and marking

• marks can make the animals more visible to predators

Carrying capacity

maximum number of organisms that a habitat can support

Limiting factors for carrying capacity

• avaialbility of resoucres

• predation

• disease

• build up of waste

Negative feedback to ensure carrying capacity

more animals leads to → more predators attartcted to an area or more spread of disease

Population growth curve

Sigmoid curve

• exponential phase - fast rate of increase

• transitional phase - still increase but slow

• platau phase - no more increase

Exponential phase

• a lot of resources

• little predation

• no disease

• good abiotic factors

Tranistional phase

• less resources

• more preadtors introdcued

• more disease

Platau phase

• carrying capacity reached

• no more space for new organisms

Case study of population growth

Mount Saint Helens in the USA

• Volcanic eruption in 1980

• Everything wiped out no life

• Later seeds brought by wind and animals started moving back

Community

group of population living and interacting in the same area

Intraspecific relationships

Between members of the same specie - cooperation or competition

Intraspecific cooperation

• helping each other out - both benefit

• Hunting in packs - wolves

• Taking turns protecting an area - lions

• Taking care of the young when the parent has to go somewhere - bats

Intraspecific competition

• win loose - fighting within species

• Fighting for avaialbility of sunlight and space - white oak tree

• comeptition for being the alpha male - gorillas

• competition for spot on a sunny rock - lizards

Interspecific relationships

between diffrent species

Interspecific relationships: Herbivory

• snails eating lettuce

• sheep eating grass

Interspecific relationships: Predation

• lions hunting zebras

• only one specie survives

Interspecific relationships: Intespecific competition

Two species competing for the same resoucres

• lions and hyanas for zebras

• humans overfishing where sharks eat

only one specie wins

Interspecific relationships: Mutualism

Both benefit

• Zooxanthele and coral reefs

Interspecific relationships: Parisitism

pasites enter the body and rely on host cell for food

• parasites that cause malarie reproduce in human liver and red blood cell

Interspecific relationships: Pathogenicity

• Pneumonia - pathogen virus or bacteria infects another specie

• cause disease in other species

Mutualistic relationship: Legume family and rhizobium

• The root nodules of legume familiy recives nitrogen from rhizobium which can fix nitrgogen conevetring it to ammonia which works as a fertilizer for the root nodules

• In return the bacteria receive carbohydrates and a favorable environment

Mutualistic relationship: Orchidaceae and Mycorrhizae

• Orhcids cant photsynthesie hence the fungus prvides the orchids with nutrients that tehy get from decompotiion of dead organic matter via hyphae networks

• After orchid dies the fungus can use it to decompose it to recive nutrients

Mutualistic relationship: Zooxanthellae and coral polyps

• Coral polyps get carbon molecules

• Zooxanthelleae get a home and minerals and CO2

Endemic specie

only found in one area in the world

Invasive specie

intorduced to a new area from a diffrent orgin and growth of pop causes probelms for the local species

Endemic species case study: Galapagos tortoises

• Only found in galapagos island

• number started to decrease due to intoreduction of invasive specie: goats

• Introduced by humans some ran off

• They started competing for land and garzing areas outcompeting the tortoises as they reporoduced faster

• Programmes were established to cut population numbers of goast

Determining interspecific competition

• field obseravtaion: obseriving in the field

• field manipulation: removing a specie from a fields and obserivning

• laboratory experiment: investigating in a lab eg greenhouse

Prey predator case study

Canada lynx hunting the snowshie hare

• Hare pop increases

• Lynx will eat their pop increases but hare decreases

• But then lynk decreases as well as all hares were ate hence no more food to sustain

Top down population control

can occur when species feed on it

Bottom up population control

reduction by lack or resources

Control of populations

• top down

• bottom up

one is always dominant

Allelopathy in garlic mustard

• releases secondary metabolites - sinigrin

• in hibts seed germination and reduces root growth of plants in the area

Alleolopathy in microbes

• fungus: peninclin rubens

• releases into area causing death of bacteri creating a bacteria free zone