populations Flashcards
what is a species
a group of similar organisms (physical,characteristically behaviourally) that can reproduce to produce fertile offspring
how can two organisms not successfully interbreed to produce fertile offspring
have a different diploid number of chromosomes in their cells
eg
a horse has 64 chromosomes in its cells while a donkey has 62. When the haploid gametes from a horse (32) and a donkey (31) combine, the resulting zygote has 63 chromosomes
Cells that have an odd number of chromosomes are not viable. The chromosomes can not form homologous pairs during meiosis to produce gametes
how do biologists define a species
Similarities/differences in observable features (morphology)
Similarities/differences in DNA
Similarities/differences in RNA
Similarities/differences in proteins
The ability to interbreed and produce fertile offspring
then place into categories
what is a population
group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed to produce fertile offspring
do populations vary in size
yes,
it is often dependent on the environment and abiotic/biotic factors
eg
The Amur leopard (Panthera pardus orientalis), now found only in the Amur River basin of eastern Russia (having already gone extinct from China and the Korean Peninsula) has a remaining population of around 60 individuals
Although humans (Homo sapiens) used to live in separate populations, we are now widely considered as one global population of around 7,800,000,000 individuals
what is a community
Multiple populations (of different species) living and interacting in the same area
how do communities form ecosystems
by interacting with the non-living components of the environment
what is an ecosystem
The interaction between a community (the living, biotic part) and the non-living (abiotic) parts of the environment
-An ecosystem is a relatively self-contained community of interacting organisms and the environment they live in, and interact with
There is a flow of energy within an ecosystem and the nutrients within it are recycled (e.g. the carbon, nitrogen and phosphorus cycles)
There are both living (biotic) components and non-living (abiotic) components within an ecosystem
how do ecosystems vary
they are dynamic and constantly changing
Ecosystems vary greatly in size and scale
Both a small pond in a back garden and the open ocean could be described as ecosystems
Ecosystems vary in complexity:
A desert is a relatively simple ecosystem
A tropical rainforest is a very complex ecosystem
No ecosystem is completely self-contained as organisms from one ecosystem are often linked to organisms from another
For example, many birds species are able to migrate long distances to find food sources or breeding locations from various ecosystems
what is a niche
the role that a species plays within a habitat
including
The biotic interactions of the species (e.g. the organisms it feeds on and the organisms that feed on it)
The abiotic interactions (e.g. how much oxygen and carbon dioxide the species exchanges with the atmosphere)
what is a habitat
the place where a species lives within an ecosystem
how many species occupy a niche
one
what happens when multiple species occupy the same niche
If two species try to occupy the same niche, they will compete with each other for the same resources
One of the species will be more successful and out-compete the other species until only one species is left and the other is either forced to occupy a new, slightly different niche or to go extinct from the habitat or ecosystem altogether
what are some abiotic factors
-temperature- optimum temp - if go below reaction slow and require more energy for body temp maintenance - if go above - enzymes denature and less energy - pop growth is limited
-light - more light = more transpiration = more plants grow and increased capacity of animals feeding on plants
-ph - optimum pH - each individual has own - if go away from this then less energy
-wind and humdity
what are some biotic factors
Biotic factors can be split into three main types:
Interspecific competition
Intraspecific competition
Predation
Could also have disease
how is the pop size controlled
The maximum stable population size of a species that an ecosystem can support is known as the carrying capacity
Every individual within a species population has the potential to reproduce and have offspring which contribute to population growth
In reality, however, there are many abiotic and biotic factors that prevent every individual in a population from making it to adulthood and reproducing
This ensures the population size of each species is limited at some point (i.e. the carrying capacity of that species is reached)
describe max carrying graph
slow at start - limited pop size - so less reproduction
-due to different gestation lengths/ enzymes work out diff speeds
-rapid increase - optimum conditions
-The point at which the graph started to flatten out (plateau) is the carrying capacity of this population
At this point, the environmental (abiotic and biotic) factors that stop all individuals from surviving and reproducing result in the population no longer being able to grow in size - food availability
-decrease would be due to toxic waste production from organisms which kills them
what is interspecific competition
This is competition for the same resources between individuals from different species
In some cases, competition between species means that the sizes of both populations are limited
This can occur as each species has access to fewer resources and therefore less chance of survival and reproduction
This usually occurs if the two species are similarly well-adapted to the habitat
In other cases, competition between species can lead to a decrease in the population size of one of the species and an increase in the population size of the other
This can occur if one species is able to out-compete the other for resources and therefore has a greater chance of surviving and reproducing
This usually occurs if one of the species is better adapted to the habitat
what is intraspecific competition
This is competition for the same resources between individuals from the same species
For example:
When resources are plentiful, the population of grey squirrels increases
As the population increases, however, there are more individuals competing for these resources (e.g. food and shelter)
At some point, the resources become limiting and the population can no longer grow in size - the carrying capacity has been reached
what is predation
Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers who are themselves eaten by tertiary consumers
Consumers that kill and eat other animals are known as predators, and those eaten are known as prey
In a stable community, the numbers of predators and prey rise and fall in cycles, limiting the population sizes of both predators and prey
what are the components that make up an ecosystem
Biotic components
There is a constant flow of energy within ecosystems. For example, the process of feeding ensures that energy can move between organisms:
Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers, who are themselves eaten by tertiary consumers
When organisms die or produce waste products, the organic matter is broken down (decomposed) by organisms such as bacteria and fungi
Species numbers are constantly fluctuating within ecosystems, as populations decline (through death and emigration) or grow (through birth and immigration)
These factors mean that the population size of a particular species constantly varies around the theoretical carrying capacity depending on factors such as interspecific or intraspecific competition, geographical location and the time of year
Abiotic components
There is also a constant flow of nutrients within ecosystems as they are continually recycled (e.g. the carbon, nitrogen and phosphorus cycles)
Water is also constantly cycled in ecosystems via the water cycle
Other aspects of weather that can affect communities of species, including abiotic factors such as temperature and wind, are also very dynamic
describe and explain the predator/prey graph
-prey consistently higher than predator
-prey peaks before the predator
EXPLAIN
-predators eat their prey - so prey numbers are reduced
-fewer prey remain so there is greater competition for the food source
-predator pop is reduced as some of the population will not have enough food
-with fewer predators, prey numbers begin to increase as less of them are eaten
-more prey are then available as a food source so the numbers pf predators begin to increase again
-cycle continues
how do selective pressures affect populations
they regulate and control the numbers
what are density (no of pop) factors
-predators
-availability of resources
-nutrient availability
-disease/pathogenic spread
-accumulation of wastes
what are density independent factors
dont relate to the size of pop
-phenomena eg natural disaster
-abiotic factors
-weather conditons
what do ecologists want to know when investigating ecosystems
-what organisms live there
-where exactly do they live
-how many are there - abundance
what type of sampling should u use when the study area is so small that you cannot count all of the organisms present
representative sampling
what must be ensured when using sampling techniques
-sample are taken at random- so that all organims have an equal chance of being selected - this avoid bias and ensures conclusions are valid
-sample must be large enough so that they can be statistically significant and provide an estimate of the pop
what is random sampling
-do not make a conscious decision about where sample is taken so no bias as equal chance of being selected
eg study area made using tape and then using a random number generator to select co-ordinates
what is systematic sampling
-make a conscious decision where to take samples
eg use a transect over a rocky shore
what are the 4 types of transect
-line transect = tape measure or string is laid along the ground in a straight line between two poles and sampling occurs along the length of the transect
-belt transect = strip of chosen width is made through the habitat using two tapes or one tape and a quadrant
-continuous transect = the whole line or belt is sampled
-interrupted transect = samples are taken at regular intervals along the line or belt
what is a quadrat
defined area within which you collect data
-frame quadrat - wood, metal and plastic
-can be open or subdivided
-used to sample sessile organisms which are immobile or sedentary that move slowly
what things do u need to find when using a quadrat
-frequency = record how many of the quadrants contained the chosen organism
-percentage cover = an estimate of the area within the quadrant that a particular plant covers - useful when a species is abundant and difficult to account
how do u know if the sample is big enough to be representative of the whole pop
record a running mean - each time u collect data work out the mean and each time it will eventually become similar
how do u sample mobile mobile animals
mark-release-recapture
For a single species in the area:
The first large sample is taken. As many individuals as possible are caught, counted and marked in a way that won’t affect their survival e.g. if studying a species of beetle, a small amount of brightly coloured non-toxic paint can be applied to their carapace (shell)
The marked individuals are returned to their habitat and allowed to randomly mix with the rest of the population
When a sufficient amount of time has passed another large sample is captured
The number of marked and unmarked individuals within the sample are counted
The proportion of marked to unmarked individuals is used to calculate an estimate of the population size
The formula for the calculation is:
N = (n1 × n2) ÷ m2
Where:
N = population estimate
n1 = number of marked individuals released
n2 = number of individuals in the second sample (marked and unmarked)
m2 = number of marked individuals in the second sample
ethical issues of fieldwork
physical damage to the environment should be avoided
the organism should be studied in situ or if moved then put back in same place
risk managment of fieldwork
-bio, chemical or physical hazards
-appropriate clothing and footwear
-consideration of weather, tides etc
-travel arrangements
-specific health requirements
give 3 examples of other sampling equipment
Pooter
Pooters are small devices using to suck up small animals like ants
Pitfall trap
A pitfall trap is dug into the ground and a small sample of food placed inside to attract small animals.Then covered to prevent rainfall - problem larger insects may eat smaller ones or may die themselves
Net
Sweep nets are swept through long grass to catch insects. Nets are also used in kick sampling, in which a foot is used to disturb the stones or sediment of a river or stream and a net collects the sample downstream.
