Populations Flashcards
Habitat
The place where an organism lives e.g. a pond
Population
All the individuals of one species in a habitat
e.g. dragonflies in a pond
Biodiversity
The variety of living organisms in an area – e.g. this can be a single habitat or globally
Abiotic factors
An ecological factor that makes up part of the non-biological environment of an organism (physical/chemical factors) e.g. temperature, pH, rainfall, humidity
Community
All the populations of different species in a habitat e.g. dragonflies, newts, beetles in a pond
Species
A group of similar organisms that can interbreed, successfully reproducing to produce fertile offspring
Biotic factors
An ecological factor that makes up part of the living environment of an organism e.g. food availability, competition, predation
A niche
Every species occupies its own niche (the role it plays) within its habitat, this includes:
• Its biotic interactions – what it eats, what its eaten by
• Its abiotic interactions – e.g. the oxygen it breathes in, and the carbon dioxide it
breathes out
• Every species has its own unique niche – a niche can only be occupied by ONE SPECIES
Carrying capacity
•Carrying capacity is the maximum stable population size of a species that an ecosystem can support.
Population size is affected by:
• Abiotic factors (non-living) • Biotic factors (living)
Limiting factors
A factor that limits further growth of a population.
-migration
-density independent factors eg earthquake
• Three typical types of populations pyramids are:
- Stable population: birth rate = death rate
- Increasing population: birth rate > death rate 3. Decreasing population: birth rate < death rate
Intraspecific variation
• Intraspecific variation–variation within a species e.g. antibiotic resistance in a species of bacteria
Inter specific variation
Inter specific variation–variation between different species e.g. thickness of blubber in seals and sea lions
Random and systematic sampling
• Random: Sampling method in which all members of a community have an equal and independent chance of being selected
– E.g.quadrat
• Systematic: Sampling method in which data is gathered according to a system, usually at fixed intervals from a fixed point
Method for random sampling
• Createagridusingtwotapemeasures
• Create random coordinates using a random number generator
• Take samples where two random coordinates intersect
• Repeattocalculateamean
Representative sampling
Representative sampling
• The sample gives a fair and accurate representation of the whole species. There is no impact of bias or chance on the results.
Sampling bias
Sampling bias
• occurs if the sample is unrepresentative due to bias sampling technique
Sampling errors
• Selection bias: Actual selection probabilities differ from assumed selection probabilities
• Random sampling error: Variation due to randomness
• Non-sampling error: – Over-coverage
– Under-coverage
– Measurement error – Processing error
– Non-response
Quadrat(random)
-Squares of a fixed size randomly placed on ground to be sampled
-Estimating the population of sessile (stationary) or slow-moving organisms
-Simple, quick to repeat, suitable for flat ground
-Difficult on uneven terrain, cannot sample fast-moving animals
Line transect (systematic)
-Line or strip laid across area to be studied. Organisms at fixed intervals along it are counted
-Measuring the distribution of organisms along a gradient (e.g. altitude, light intensity, moisture)
-Simple, can sample across a range of habitats in an ecosystem, shows change in abiotic factors too
-Can be time- consuming, distance from transect must be maintained, cannot sample fast-moving animals
Mark and recapture
-Members of a population are caught, counted, marked, and released
-Estimating the population of fast- moving or difficult- to-see animals
-Can be used for fast-moving animals
-Very time- consuming, difficult not to just catch sick/weak specimens
What does skewed mean
If median, mode, and mean are not equal, distribution is said to be skewed
Why scientists use sampling techniques
• Too many organisms to count
• Cannot find all organisms
• Area too large to study
• Too time consuming
Why might we want to sample an area
• Curiosity/scientific endeavour • Conservation
• Sustainability
Mark release recapture method
- Capture a sample of the animal, using an appropriate technique
- Mark them in a harmless way (count how many you have caught)
- Release them back into their habitat
- Wait a week, and resample the same population
- Count how many of the second sample are marked
- Use the Lincoln Index to estimate the total population
Lincoln index
(n1 ×n2)÷n3 =total population
-n1 first capture
-n2 second capture
-n3 recaptures
What are the limitations of a capture- mark-recapture system?
• Accuracy depends on capturing a fairly large proportion of the population.1
• Many study populations arenot geographically closed because only a part of a population’s range is included in the study area.
• Animals can move into and out of some study areas, and the number of animals present at a given time may be less than the population estimated
What assumptions do we have to make about our sampling technique and the population we are sampling for the Mark- release-recapture method?
- During the study period, births, deaths and migration rates have remained stable (Why can’t we say NO BIRTHS/DEATHS?)
- The mark doesn’t affect how well the individual survives – make it stand out to predators/toxic
- The mark doesn’t rub off
- The marked individuals have enough time to mix back into the population
Ecosystem
More or less self contained unit in ecology made up or biotic and abiotc factors
Community
All the populations of different species living and interacting together in a particular area
Primary succession
Primary succession – on land that is newly formed or exposed. No organic material or soil there at the start.
Secondary succession
• Secondary succession – soil is present but no plants or animals.
Deflected succession
• A community that remains stable only because human activity prevents succession from running its course.
• This happens all the time, for example, sheep grazing prevents grassland from developing into woodland.
• Many places need to be actively managed in the battle against succession, for example, golf courses need to be mowed all the time
• It is called a plagioclimax as succession is stopped artificially
2 types of competition
Intraspecific – between individuals of same species
Interspecific – between individuals of different species
Competition
• Competition is:
– a struggle between individuals for
resources (like food & water) that are in limited supply
• Competition decreases reproduction rate (fewer resources to support reproduction) but increases death rate (fewer resources to support survival)
Interspecific competition
• When the population size of one species changes so does the other.
• Generally has a pattern of 4 stages:
1. Increase in prey – more food for predators
2. Increase in predator – means decline in prey population
3. Less food available for predators – competition leads to a reduction in predator population size
4. Less predators – more prey are able to survive, increase in prey
