Chapter 19 - Populations in ecosystems Flashcards
What is ecology?
Studying the inter-relationships between organisms and their environment
What are abiotic factors?
Non-living
What are biotic factors?
Living
What are the two major processes to consider in an ecosystem?
The flow of energy
The recycling of elements
What is a population?
A group of individuals of one species that occupy the same habitat and have the potential to interbreed successfully
What is carrying capacity?
The size of a population an ecosystem can support
What is a community?
Different populations living and interacting in the same area at the same time
What is a habitat?
The place where an organism usually lives
What are microhabitats?
Smaller units within a larger habitat, each with its own microclimate
What is a niche?
How an organism fits into its environment
What are adaptations?
Features that increase the chances of a species surviving and reproducing
Examples of adaptations to abiotic conditions (3)
Webbed paws - live and hunt on land and in water
Blubber - live in colder places with more food
Hibernation - conserves energy during cold months
Examples of adaptations to biotic conditions (2)
Bacteria produce antibiotics to kill off competition
Mating call - attracts members of the same species
What is population size?
The number of individuals in a population
Give two reasons why a population may fluctuate
The effect of abiotic factors
Interactions between organisms
In what instance is it useful to use a logarithmic scale?
Where the population grows rapidly over a short period of time
How does a logarithmic scale differ from a normal one/
Log(population) is plotted rather than the population itself
Give three reasons why a population may start to level out
Consuming and using up mineral ions
Winter brings lower temperatures and levels of light intensity
Bacteria collect at the surface and prevent light reaching those at the bottom
What are the four abiotic factors that influence the size of a population?
Temperature, pH, light intensity and water/humidity
How does temperature influence population size?
Enzymes - too low means there’s less kinetic energy for successful collisions and too high denatures the enzyme
Warm blooded organisms have to expend energy in maintaining their temperature levels
How does light influence population size?
Photosynthesis - more light means more photosynthesis. This increases their carrying capacity so more animals can survive
How does pH impact population size?
A pH other than the optimum releases H+ or OH- ions which interfere with and disrupt the hydrogen bonds
How does water/humidity impact population size?
Too dry means that more evaporation occurs, so there is no growth or food produced
Too wet means that special adaptions are required to survive and so diversity is reduced
What are the two types of competition?
Interspecific and intraspecific
What is intraspecific competition?
Individuals of the same species competing for resources
How does intraspecific competition impact a population?
The availability of resources determines the carrying capacity, and so population size
What is interspecific competition?
Individuals of different species competing for resources
How does interspecific competition impact a population?
Because the two species are occupying the same niche, one will have a competitive advantage over the other. This population will grow whilst the other will shrink and finally disappear
What is the competitive exclusion principle?
Where there are two species occupying the same niche, one will normally have a competitive advantage
The population of this species will grow and the population of the other will diminish
Conditions remain the same, leading to the removal of one species
When you are explaining how a factor influences population size, what is it important to link your explanation to?
The birth/death rate
What is predation?
One organism consuming another
Why is data gathered on predation in a lab generally not representative?
In the lab, the prey is usually exterminated by predators. This is because the size and type of habitat available is much smaller and less varied than in nature. There are also many more refuges in nature so although the prey population may fall to a low level, it rarely becomes extinct
What effect do predators and prey have upon eachother?
Predators eat prey, reducing the prey population
The predators are in greater competition with each other for the prey that remains
The predator population then falls as there isn’t enough food to support a larger population
Fewer prey are eaten and so reproduce to rebuild their population
The predator population increases as there is more food sources
Why is the graph showing predator-prey cycles normally exaggerated?
In natural ecosystems, predators normally eat a range of prey rather than just the one species
What other factors can influence a population?
Disease and climate
Why is the cyclical relationship of predators and prey important?
The crashes in populations are important in evolution as they create selection pressures and only those adapted to the conditions can survive
What is abundance?
The number of individuals in a specific area
What are the two types of sampling we use?
Random and systematic
What are the two types of quadrat?
A point quadrat and a frame quadrat
What is a point quadrat?
A horizontal bar supported by two legs. There are holes along the length of the bar, through which a pin is placed. The species touching this pin is then recorded
What is a frame quadrat?
A square frame divided into equal subdivisions
What are the three factors to consider when using quadrats?
The size of the quadrat to use
The number of quadrat samples to conduct
The position of each quadrat in the study area
Why is it important to consider the size of quadrats used?
The size must be appropriate to the size of the area being studied
To get a representative sample, it is normally better to use a larger number of smaller quadrats
Why is it important to consider the number of quadrats used?
The greater the number of quadrats used, the more reliable and representative your results will be. However, this is a time consuming process
Why is it important to consider the positioning of each quadrat?
Random sampling must be used to avoid bias and make your results reliable
How do you conduct a random sample of an area?
Lay two long tape measures at right angles to eachother
Use a random number generator to generate your coordinates
Place the quadrat at the intersection of these coordinates and record the species inside it
How do you conduct systematic sampling of an area?
Lay out a long piece of string across the area you wish to study
Lay down a frame quadrat at the beginning of the string
Record the species inside the quadrat
Move the quadrat its own distance down the string and repeat the process
What is abundance?
The number of a species in a given area
What are the two common measures of abundance we use?
Frequency and percentage cover
When is percentage cover useful?
When a species is particularly abundant or difficult to count. This is because the species don’t need to be counted individually and can be conducted fairly quickly
What is percentage cover?
An estimate of the area within a quadrat that a particular species occupies
What is frequency?
The likelihood of a species appearing in a quadrat
When is frequency useful?
It is quick and gives information about the general area of a species, particularly when it is difficult to count
When is calculating frequency not useful?
It doesn’t provide information on the density of a species or its positioning
When are transects and quadrats not useful?
For mobile animals
What method is used to calculate the abundance of animals?
Mark-release-recapture
What is the equation for mark-release recapture?
Population size = (total number of individuals in the first sample x total number in the second sample) / number of marked individuals recaptured
What are the six assumptions made for mark release recapture?
Mark is not rubbed off
Few deaths and births within the population
Method of marking isn’t toxic/makes the animal more susceptible to predators
No emigration or immigration
The marked individuals have sufficient time to redistribute themselves throughout the population
The proportion of marked: unmarked individuals in the second sample is the same as the proportion of marked: unmarked in the total population
What is conservation?
Managing the earth’s natural resources by humans in such a way that maximum use of them can be made in the future
What does conservation aim to preserve?
Ecosystems and biodiversity
What are the four main reasons for conservation?
Personal, ethical, economic and cultural and aesthetic
Why do we conserve the planet for personal reasons?
We are supporting our life system
Why do we conserve the planet for economic reasons?
The organisms we conserve have a huge pool of genes, which enable the plants to make many of the substances we use and profit from all the time
Why do we conserve the planet for ethical reasons?
We should respect the living organisms that have been on earth longer than us
Why do we conserve the planet for cultural reasons?
The variety of organisms and habitats enriches our lives
Why might a pioneer species not feature in a climax community?
Their habitats have disappeared because of succession or they have been out competed
How do we conserve the planet by managing succession?
We put factors in place to prevent further succession, and so removal of habitats
What is succession?
The changes that occur to a particular ecosystem over time
What is primary succession?
Occurs on land that has just been formed or exposed - there is no soil or organic material to start with
What is secondary succession?
Occurs on land that has been cleared by humans but some soil and organic material remains
Which type of succession is faster and why?
Secondary succession - there is already some existing organic matter and soil so different species can be supported
What is important to remember when considering succession?
Competition!
What is a pioneer species?
A species that is adapted to living in extreme conditions and can start to colonise an area
What are some of the adaptations that a pioneer species might have?
Asexual reproduction
Rapid germination of seeds
Tolerance of extreme conditions
Ability to photosynthesise and grow own food
Describe the process of succession
1) Pioneer species - the first species to colonise an area. Have adaptations to withstand extreme conditions
2) Pioneer species penetrates and breaks up the rock. As the species dies and decomposes, a layer of humus builds up, allowing simple plants to grow
3) These plants cast shade, preventing the pioneer species from growing. They have longer roots and so can break up even more rock. As they die, the amount of nutrients and water in the soil increases, so more complex plants can be supported
4) Larger plants grow so animals can inhabit them. This changes the soil and light conditions, killing the smaller plants
5) A climax community is reached and dominant plant species colonise an area
What is the most common climax community in the UK?
Oak woodland
How to calculate the mean density
Total number of individuals counted /
total number of quadrats x area of one quadrat
What are the two factors that impact the succession of animals?
Habitats and food sources
How does succession in animals occur?
Over time, more complex animals can be supported by organic matter. This means that there are more food sources and larger animals come to the area
What five common features emerge during succession?
The abiotic environment becomes less hostile More habitats and niches Increased biodiversity More complex food webs Increased biomass
