3.5 -Population Size And Ecosystems Flashcards
Define population
An interbreeding group of organisms of the same species occupying a particular habitat
Define birth rate
The reproductive capacity of a population; the number of new individuals derived from reproduction per unit time
Define immigration
The movement of individuals into a population of the same species
Define equilibrium species
Species that control their population by competition rather than by reproduction and dispersal
Name factors in an ecosystem that affect all organisms living in it, these factors are constantly changing, so ecosystems are dynamic:
1) intensity if energy flowing through the ecosystem varies
2) biological cycles such as the nitrogen cycle vary mineral availability
3) habitats change over time as succession occurs
4) new species arrive and done speacies are no longer present
How can the size of a population at a particular time be determined?
1- birth rate (increase pop)
2- death rate/ mortality (decrease pop)
3- immigration (increase pop)
4- emigration (decrease pop)
When does a population size increase
When the combined effects of birth and immigration exceed those of death and emigration the population size increases
What are fugitive species?
Species that are poor at competition, instead they rely on a large capacity for reproduction and dispersal to increase numbers.
They invade a new environment rapidly e.g algae colonising bare rock
What are equilibrium species
A species which control their population by competition within a stable habitat. Their usual pattern of growth is a sigmoid (s-shaped) curve called the one step growth curve.
Example: when bacteria are put into fresh nutrient solution
What are the 4 stages of the one step growth curve?
- Lag phase
- Exponential log phase
- Stationary phase
- Death phase
Define the term environmental resistance
Environmental factors that slow down population growth
Define biotic
A part of the environment of an organism that is living e.g pathogens or predators
Define abiotic
A part of the environment of an organism that is non living e.g air temperature or oxygen availability
Define carrying capacity
The maximum number around which a population fluctuates in a given environment
Describe the lag phase
It is a period of adaptation or preparation for growth with intense metabolic activity where there’s slow growth in population.
Describe the exponential phase (log phase)
As numbers increase (as long as there’s no factor limiting growth) more individuals become available for reproduction. E.g bacterial cells divide at a constant rate per unit time (cell number increases logarithmically) :: also called log phase
Why can’t the exponential phase be maintained?
Environmental resistance sets in:
- less food available
- concentration of waste products becomes increasingly toxic
- not enough space or nesting sites
(The population still increases but more slowing so the gradient of the graph decreases)
Name environmental resistance factors affecting the growth of bacteria in a flask:
1- available nutrients
2- overcrowding
3- competition
4- accumulation of waste
Name some biotic factors that affect non artificial environments e.g rabbits on an island
1- all environmental resistance stated previously
2- predation
3- parasitism and disease (increased population density allows disease to spread more rapidly)
4- competition from other species for nesting/food sites
Name some abiotic factors affecting non artificial population size
1- light intensity
2-temperature
Describe the stationary phase
- Occurs when the birth rate = death rate.
- the population has reached its carrying capacity for that particular environment
- actual number depends on resources available e.g more food = higher carrying capacity
- the population is not absolutely constant and fluctuates around the carrying capacity based on environmental changes e.g number of predators
Describe the death phase
The factors that slow population growth at the end of the lag phase become more significant and population size decreases until the death rate is greater than the birth rate and the graph has a negative gradient
Describe the effect a predator-prey relationship has on a population
1- causes both populations to oscillate which are regulated by negative feedback
2- predators are normally larger than prey
3- the abundance of prey limits the numbers of predators and the number of predators controls the numbers of prey
Describe the predator prey relationship between lynx and hares
1- a large number of lynx predate hares, so the hare population decreases
2- there is not enough food for the lynx so lynx numbers decrease
3- there is less predation on the hares so hate numbers increase again
4- there is more prey for lynx so lynx numbers increase
What is a density dependent factor? Give examples
Environmental factors thay have more effect if the population in a given area is larger.
These biotic factors include disease, parasitism and depletion of food supply
E.g If a population is denser parasites are transmitted more efficiently
What are density independent factors?
They are abiotic f acc tor’s which do not depend on the population density. The effect is the same regardless of the size of the population, and is usually a sudden abiotic change e.g fire or flood.
Describe how population size is regulated by negative feedback
If the population rises above the carrying capacity a density dependent factor increases mortality or reduces breeding to an extent where the population declines
If the population falls below the carrying capacity environmental resistance is temporarily relieved so the population rises again
Define biogeography and explain its founder
The study of species abundance and distribution, coined by Alfred R Wallace who modelled 6 biogeographic regions and saw different animals in similar habitats which contributed to his understanding of natural selection.
Why are physical features e.g soil type and temperature first described when a new habitat is assessed?
Because they determine the number and types of organisms that live there e.g a very cold habitat may support only lichens but a warmer habitat may support a vast number of animals
Define the term abundance
The number of individuals in a species in a given area/volume
How can animal abundance be assessed?
1) capture mark recapture experiments using the Lincoln index calculation
2) kick sampling in a stream and counting aquatic invertebrates
How can plant species abundance be assessed
1) using a quadratic to calculate the mean number of individuals in several quadrants of a known area, to find the density (number/m squared)
2) estimating % cover of a plant in which individuals are hard to recognise
3) estimating % frequency
Define the term distribution
The area or volume in which the organisms of a species are found
How do you measure the distribution of a species if the habitat is uniform?
What does a small area indicate?
Why is this technique used?
- Mark the position of the outermost plants on a map and the area they surround can be measured.
- A small area indicates the species may under threat of extinction
- botanists use this technique to assess the distribution of threatened plant species so they can protect specific sites against mining companies/road building mitigating species loss.
What does a line transect show?
Shows the organisms that lie on a line at measured intervals (pg 70 for example)
What does a belt transect show?
The abundance data for a given area at measured distances along the transect. A quadratic is placed at each co-ordinate along the transect and readings are taken for:
- the density of chosen species
- % frequency of chosen species
- % area cover for all species
What diagram can be drawn to show the % cover of a species along a belt transect?
A kite diagram
If a transect is positioned horizontally along a footpath what can the species distribution in the kite diagrams/ line/belt transect show?
Can show which species are more resistant to tramping because they still grow in the middle of the path/ most sensitive to trampling as they grow on the outer edges of the path.
Why are belt transects represented in kite diagrams better than line transect?
They are better because they are two dimensional which provides more information about species distribution and abundance than the one dimensional line transect.
However numbers are rounded when kite diagrams are drawn so accuracy is lost in comparison with a table of data.
What are transects suitable for measuring?
What are transects not suitable for measuring?!
Suitable: plants, sessile animals
Not suitable: motile anomalies because they move.
Name ways of measuring animal distribution
1- direct observation of individuals or their nests
2- faecal deposits
3- markings
4- vegetation
Define the term ecosystem
A characteristic community of interdependent species interacting with the abiotic components of their habitat
Give an example of a small ecosystem, large ecosystem, long lasting ecosystem and temporary ecosystem
Small= humans large intestine and it’s community of micro-organisms
Large= seas cover about 70% of the earths surface and the Pacific basin is the largest marine ecosystem
Temporary= puddle left after the rain
Long lasting= Lake Baikal in Siberia has existed for 25 million years
Give an example of a marine ecosystem, it’s abiotic and biotic feature
Example: Pacific Ocean
Abiotic features: high mineral salt concentration
Biotic features: algae, starfish
Give an example of a arctic tundra ecosystem, it’s abiotic and biotic feature
Example: Siberia
Abiotic: temperatures between -50 and 12 degrees Celsius
Biotic: moss, arctic hare
Give an example of a desert ecosystem, it’s abiotic and biotic feature
Example: Sahara
Abiotic: less than 25cm rainfall annually, high temperatures & light intensity
Biotic: cactus, camel
Define the term energy
The ability to do work, no change happens unless energy changes occur.
What is the law of thermodynamics?
The functioning of an ecosystem can be thought of as a sequence of energy changes in which energy flows through the components of the ecosystem subject to rules.
Name some examples of energy source on earth
1) Geothermal energy
2) Electrical energy
3) Chemical energy (early organisms used energy released in chemical reactions to make carbohydrates via chemiosmosis)
4) Light energy (significant as it radiates from the sun providing energy for photosynthesis)
Define the term habitat
The place in which an organism lives
Define the term community
Interacting populations of two or more species in the same habitat at the same tine
Define the term trophic level
Feeding level, the number of times that energy has been transferred between the sun and successive organisms alone a food chain
Define the term biomass
The mass of biological material in living or recently living organisms
Define microhabitat
A very small area that differs from its surroundings and has the features that make it suitable for a particular species
E.g the cabbage looper feed on the lower surface of leaves of cabbages
What does a habitat provide for an organism?
A means of survival such as food, water, soil, appropriate temperature and pH.
What does community ecology study?
Studies the interactions of species related to their:
- distribution and abundance
- genotype and phenotypic differences
- considered food web structured and predator-prey relationships
What is ecological energetics?
The study of the flow or energy through the ecosystem
What do photosynthetic organisms do?
Convert sunlight energy into chemical energy which passes from one organism to the next along a food chain.
How are food chains and biomass related?
The energy available to a trophic level contributed to its biomass and hence food chains can be thought of as a means of transferring biomass.
What are producers (give examples) and describe their role in the food chain
Green plants, Cyanobacteria and some protoctista are producers because they incorporate the suns energy into their carbohydrates which are the food and energy source for successive organisms in the food chain.
They trap solar energy and synthesise sugars from inorganic compounds by photosynthesis
What should I note about the proportion of light energy that is stored in producers
Only a small proportion of the total light energy that reaches the plant is incorporated into the plants tissue as some is reflected/used to evaporate water.
What are primary consumer?
Herbivores. They are animals that feed in plants
Describe the consumer role of carnivores
They are secondary, tertiary and higher consumers, they are animals that feed on other animals.
What’s important to know about energy transfer between trophic levels?
Energy in the food consumed is incorporated into the molecules of the consumer
As energy is passed along the food chain from one trophic level to the next there is a loss of energy, and the energy flowing through the ecosystem reduces and ultimately the energy leaves the system as respiratory heat.
Define the term saprobiont
A micro-organism that obtains it’s good from the dead or decaying remains of other organisms
What happens to the energy when producers or consumers die?
The energy remains in the organic compounds of which they are made
Detrivores and decomposers feed as saprobionts (derive their energy from dead and decaying organisms) and contribute to the recycling of nutrients.
What are detritivores?
Organisms (such as earthworms woodlice and millipedes) which feed on small fragments of organic debris (detritus; the remains of dead organisms and fallen leaves)
What are decomposers?
Microbes (such as bacteria and fungi) that obtain nutrients from dead organisms and animal waste. They complete the process of decomposition started by detritivores.
Sum up a detritus food chain:
Detritus—> detritivore —> decomposer
Define the term food chain. Give an example
A linear sequence of organism in a food web.
Grazing food chain example:
Producer —> primary consumer —> secondary consumer —> tertiary consumer
Note that there is 4 trophic levels present
What does a food web show?
Shows how the organisms in a community interact with each other through the food they eat
Why is the number of links in a food chain normally limited to 4/5?
Energy is lost at each link along the food chain and :: after link 4/5 there is not enough energy to support one another.
What are factors that can limit the length of a food chain?:
1- the more energy that enters a food chain in the first trophic level the longer the chain can be :: food chains which have high light all year tend to be longer than arctic food chains
2- the more efficient the transfer of energy between trophic levels the longer the food chain
3- predators and prey populations fluctuate and their relative abundance can affect the food chain length
4- larger ecosystems can support longer food chains
What factors can increase the leaf efficiency in absorbing energy per unit area?
If it is thicker, has a thinner cuticle, more chloroplasts, more chlorophyll and more grana.
About 60% of light energy that falls on a plant may not be absorbed by photosynthetic pigments due to:
- light being the wrong wavelength
- light being reflected
- light being transmitted straight through the leaf
What is the photosynthetic efficiency (PE) equation?
PE= Quantity of light energy incorporated into products/ Quantity of energy falling on the plant
X100