C4.1 Flashcards
What is a population?
Group of species that live in the same area
Can interbreed, interbreed less or never
Geographically separated
What is a community?
A group of many different species populations live in the same area
What are some examples of non-breeding interactions?
Competition -.> resources
Cooperation -> avoid predation
What is the use of random sampling?
Used to estimate the size of a population.
Estimations based on evidence
Rare to count reliably (camouflage, movement)
sampling
Small portion
Not a representative of whole population -> use multiple samples
Every individual should have an equal chance of inclusion -> random sampling
Estimate
Based on evidence, assumptions
For population size -> sampling
What is random sampling?
Every member of a population -> equal chance of selection
Unconscious bias avoided
Use of random numbers for this reason -
quadrats
Square sample areas -> marked with frame
Quadrat sampling -> place frame -> random positions in habitat -> record no. organisms present
Random coordinates generated -> place quadrat in area sampled -> each area must have equal chance
how to calculate a population estimate?
Population estimate = mean count per quadrat x area of whole site / area of one quadrat
Only suitable for sessile organism (fixed positions)
What is the capture-mark-release-recapture method? To estimate population sizes?
Capture as many -> in area occupied with netting, trapping, searching
Mark each, without making them visible to predators
Release back into habitat
After a day/two, recapture as many, count the marked and unmarked
What is the Lincoln Index
used to estimate population sizes
M x N / R
M=no. individuals caught+marked
N = total number recaptured
R = total number recaptured with marks
What are some assumptions from the period of time from capture to recapture?
No migration in/out
No deaths/births
Marked individuals mix back -> same chance of being captured second occasion as non marked
Marks remain visible
What is carrying capacity?
Maximum population size of an environment can support
- resources are needed, e.g food, limited
What happens when a resource becomes scarce?
-Competition for it by members of a population
-if population is too large, some are unable to attain
Examples of resources that will limit carrying capacity?
Animals
- water
- space for breeding
- food/territory to obtain food
- dissolved oxygen in water
Plants:
- water
- light
- soil nitrates and phosphates
What factors cause changes in population size?
Density dependent factors
Density independent factors
What are density independent factors
Same effect whatever populations size (e.g frost vs plants, forest fires)
what are density dependent factors?
Increasing effect as population becomes larger
Negative feedback mechanisms -> reduce larger populations/smaller populations increase
Tend to bring back to carrying capacity
What are the three groups of density dependent factors?
Competition - resources are limited
Predation - if the predator population is denser, they are easier to find. If scarce, this is less intense
Infectious disease, parasitism, pest infection -> increase with density, transfer to host to host is easier if closer
What factors contribute to a change in the number of individuals in a population?
Natality - offspring produced+added
Mortality - individuals die+lost
Immigration - individuals move into area from elsewhere
Emigration - individuals move from area to elsewhere
How can we calculate the overall change in the size of a population?
Natality + immigration - Mortality + emigration
What is a sigmoid (S-shaped) population growth curve:
To show increased population size over time
phases:
exponential
transitional
plataeu
Explain the exponential part of the Sigmoid population growth curve?
population is established in an ideal environment -> follows exponential growth pattern -> increase rapidly
-> natality rate > mortality -> Resources abundant
pred/diseases rare -> Immigration > emigration
Explain the transitional part of the Sigmoid population growth curve?
Slows, carrying capacity is reached -> max population -> natality falls -> mortality rises -> natality is still larger but by a lowering amount
Explain the Plateauing part of the Sigmoid population growth curve?
factor limits -> population
-> shortage + more predators + disease + pests
-> negative feedback mechanism, as population rises, density dependent factors are more intense
- emigration > immigration
Outline a test to model the sigmoid population growth curve
1) Test whether model -> fits growth real population
2) Small no. individuals -> given abundant resources -> numbers counted at regular intervals + repeats
3) Floating plants (e,g duckweed) -> grown on water in beakers
4) contain nitrate, phosphate + mineral ions needed
5) placed in bright light -> warm temp -> suitable rapid growth
6)No. counted on surface -> Exp continued until one resource needed is limiting
What is an intraspecific relationship?
One that exists between individuals of the same species + usually in same population
Intraspecific competition
Members, population -> same ecological niche -> same resources required
If abundant -> no competition -> vise versa
Some more successful -> gain more resource -> survive + reproduce
Natural selection over generations for traits -> for individuals to compete effectively.
Intraspecific cooperation:
Individuals, population -> cooperate -> extent varies -> e.g termites
All individuals benefit
interspecific relationships
One that exists between individuals of different species
Divided in two groups
What are the relationships between species not living in close association?
Herbivory
Predation
Interspecific competition:
Herbivory
Primary consumers -> feed -> producers (may/not be killed
Bison feeding on grasses
Predation
One consumer species kills/eats another consumer species (prey)
Anteaters feeding on ants
Interspecific competition:
two/more species use the same resources, rivalrous
Ivy competing with oaks
What are the Relationships between species living in close association:
Mutualism
Pathogenicity:
Parasitism
Mutualism
Two species -> close association -. Benefit from this
Zooxanthellae in hard corals
Usually from different taxonomic kingdoms -> different capabilities + different services.
Pathogenicity
One species (pathogen) lives inside another species (host) -> disease
Anthrax bacteria in kudu (african antelope)
Parasitism
One species (parasites) lives in/on another species (host) -> obtains food -> host harmed, parasite benefits
Black legged ticks on white tailed deer
Examples of mutualism
Root nodules in Fabaceae (legumes)
Mycorrhizae in orchids (orchidaceae)
Zooxanthellae in hard corals
Root nodules in Fabaceae (legumes)
Mutualistic relationship -> rhizobium bacteria
grows a root nodule -> bacteria can safely live
Provide sugars + low o2 environment -> rhizobium convert nitrogen -> ammonium ions -> some supplied to plant -> promoting growth in low nitrogen soils
Mycorrhizae in orchids (orchidaceae)
Hyphae of Russula + other mycorrhizal fungi -> grow -> roots -> penetrate root cell walls
Fungus -> extension of root system -> absorbs water + mineral nutrients -> passed to orchid
Orchid -> supplies sugars + carbon compounds -> photosynthesis
Zooxanthellae in hard corals
- Cells of reef-building hard corals -> zooxanthellae (algae) -> absorbed from seawater
- In safe environment gain co2 (aerobic respiration) from coral cells
- Use in photosynthesis, coral -> gain o2, carbon compounds + aminos -> produced from photosynthesis
Endemic versus alien species?
Species that occur naturally in an area vs species that were introduced by humans are alien.
What happens if alien species are not effectively regulated?
pests/predators in their native habit are absent
If they increase in number, and spread rapidly -> invasive .
Alien species -> successful -> competition of resources
What is the competitive exclusion principle?
Predicts that two species cannot occupy the same ecological niche indefinitely (no two species can exploit in the same way)
COMPETITION -> same/overlapping ecological niches
Consequences of invasive species?
Endemic species -> occupy smaller realized niche
Decline in pop
Lose its niche entirety
Extinction
Widespread -> humans transport high no. (species) to new areas -> not enough/no limiting factors to control populations of alien species.
Approaches to test interspecific competition:
Field manipulation -> one of two species removed from quadrats -> evidence of interspecific competition -> if increase in no. or biomass
Laboratory experiments -> under controlled conditions -> species grown together + apart -> investigate if they compete
Tests for association between species -> random sampling
What is the chi squared test?
Test for association -> are twos pieces found in same/diff quadrats, or are they randomly distributed?
outline the chi squared test…
1) Define two alternative hypotheses:
2) Draw a contingency table of observed frequencies (containing/not containing species)
3) Calculate expected frequencies for the 4 species combinations, assuming independent distribution
4) Calculate number of degrees of freedom (df)
5) Find critical region using table of chi-squared values and probability = 0.05 (5%)
6) calculate chi squared
7) If the calculated value is in critical region, there is evidence at the 5% level -> association between two species
expected frequency formula
Expected frequency = row total x column total / grand total
number of degrees of freedom
Df = (m-1)(n-1)
m=rows
n= columns
what happens if df = 1?
the critical value is 3.83 or larger
calculate chi squared
what happens If the calculated value is in critical region
there is evidence at the 5% level -> association between two species
- reject null hypothesis
- Species are found more/less frequently -> than if randomly distributed
- Tend to occur together in quadrats when they have same habitat requirements -> or interspecific relationship -> encourages co-location.
- Tend to occur in different quadrats -> may be competition for resources or different habitat req.
what are predator prey relationships?
Population of prey does not change much due to predation -> new individuals born at same rate as lost
Rates are stable for both predator+prey
Dynamic equilibrium
Some do not have dynamic equilibrium -> cyclical oscillations in numbers -> possibly due to habitat weather conditions varying
What are the 4 types of density dependent interactions?
Rise in prey -> increase prey availability -> predator rise
Fall in prey -> fall in availability -> pred falls
Rise in pred -> prey falls -> pred increase
Fall in predator -> prey rise -> pred decreases
What are Two Types of interactions operating in control of populations?
Top down control acts -> higher trophic to lower
- increase in pred -> decrease in prey in lower trophic levels
Bottom up control -> lower to higher
- Population of producers limited by mineral nutrient availability
What are secondary metabolites?
Substance produced by a pathway, exists in some taxonomic groups
Not essential for cell growth -> wider range of functions
Released to environment -> toxic to other organisms and deter potential competitors
What are antibiotics?
Secreted by microorganisms -> kill -. inhibit/prevent growth of other species of microorganism.
E.g penicillium
What is penicillium?
Fungi inhabits natural habitats -> saprotrophic
the food they digest -> may be absorbed by bacteria
Penicillium -> secrete penicillin -> Reducing competition
Interferes with cross-linking of peptidoglycan molecules -> cell wall of gram-positive bacteria
Walls -> weak -> eventually burst and die
What is allelopathy:
the chemical inhibition of one organism due to another
-> chemical release into the environment of substances acting as germination or growth inhibitors.
What are allelopathic agents?
Secreted to soil -> plants -> to kill/deter growth of neighbouring plants
Reducing competition for water/mineral ions
What is ailanthus altissima (tree of heaven)
Native to China
Invasive species across NA
Released Ailanthone -> soil -> inhibits germination, growth, survival -> Of other trees
