Flashcards in 1. Populations Deck (46)
Suggest an explanation for the change in the percentage of deaths due to cancer shown in the diagram
-Decrease in percentage of population dying from infectious diseases
-Therefore greater proportion of those remaining die of cancer
-Greater survival to old age so cancer more likely
-Because of accumulated genetic error/ exposure to mutagens/ reduced immune response
What would an age pyramid look like for a population that had a life expectancy at birth of 70 years
Narrow based population pyramid
Explain how two changes in social conditions could have reduced the death rate
-Better food supply so fewer deaths by starvation
-Cleaner water supply so less disease transmission.
Give two possible reasons for fluctuating death rate
-Epidemics/ outbreaks of disease
-Limited/changing food supply
Suggest three reasons why the rapid increase in human population has resulted in the reduction of populations of many other species
-Predation of other species/ eat more of other species
-Interspecific competition/ disruption of food chain
-Destruction of habitat/damage by pollution
-Niche not present
-Competition for named abiotic resource
Give examples of abiotic and biotic factors.
Define an ecosystem.
-Made up of all the interacting biotic and abiotic factors in a specific area. Very often a self contained, self functioning unit
a large naturally occurring community of flora and fauna occupying a major habitat, e.g. forest or tundra.
Define a population.
A group of interbreeding organisms of a particular species in a habitat.
Define a community.
All the populations of different organisms living and interacting in a particular place at the same time.
Define a habitat.
The place where a community of organisms lives
What is a microhabitat?
A smaller unit within a habitat with its own microclimate.
What is an ecological niche?
A niche describes how an organism fits into the environment- where it lives and what it does there.
What are the three factors to consider when using quadrats to sample an area?
-SIZE of quadrats to use- depends on size of species being counted and how they are distributed
-NUMBER of sample quadrats to record within the study area- larger numbers means more reliable results
-POSITION of quadrats within the study area- random sampling must be used to produce statistically significant results.
Why is random sampling important?
-Ensures data obtained are valid
How do we make sampling random?
-Make a grid by laying out two tape measures perpendicular to eachother
-Obtain coordinates using a random number generator (generated by a computer or using a random number table)
-Place a quadrat at the intersections of coordinates and sample at that point
Why would systematic sampling along a transect be used instead of using a quadrat to randomly sample?
-When you want to measure the abundance and distribution systematically when some form of transition in the organisms takes place- for example, measuring the stages of zonation.
What are the two ways abundance can be measured?
-FREQUENCY- counting whether a species is present in a quadrat or not
-PERCENTAGE COVER- estimate of area within a quadrat that a particular plant species covers
What is the equation to work out the estimate of a population size using the mark-release-recapture method?
Estimated population size= (total number of individuals in the first sample) X (total number of individuals in the second sample) / (number of marked individuals recaptured)
What are the assumptions we make in the mark-release-recapture technique?
-Proportion of marked:unmarked in the second sample is the same as marked:unmarked in the total population
-Marked individuals distribute homogeneously
-No immigration or emigration
-No births and deaths within the population
-Marking is not toxic or makes it more liable to predation
-Mark is not rubbed off
Describe the graph of the phases of the usual pattern of growth for a natural populations.
-STAGE 1 period of slow growth-small number of individuals reproduce to slowly build up their numbers
-STAGE 2 Log phase- exponential growth where increasing number of individuals continue to reproduce
-STAGE 3 stable phase where rate of growth declines until the size of the population is more or less stable with small fluctuations
What are the abiotic factors that influence the size of a population?
-Temperature- species have an optimum temperature, above it enzymes may denature and below it enzymes will not function fast enough
-Light- the ultimate source of energy in an ecosystem
-pH- affects the action of enzymes
-Water and humidity- affects transpiration in plants and evaporation in animals
Describe intra-specific competition
Competition between individuals of the same species for:
Describe inter-specific competition.
What happens when two species occupy a similar/ the same niche?
When individuals of different species compete for food, light, water etc.
The species better adapted will effectively eliminate the other species as no two species can occupy the same niche.
Describe the stages of a predator-prey cycle.
-Predators eat prey, thereby reducing the population of prey
-Predators in greater competition due to reduced prey
-Predator population is reduced as some individuals not able to obtain sufficient food for survival
-With fewer predators, fewer prey are eaten
-Prey population therefore increases
-More prey available means the predator population increases
Give 3 reasons for cyclic fluctuations in populations
-Predator prey cycles
What is selection pressure?
The well adapted individuals are more likely to survive to reproduce (withstand disease, escape predators etc...)
What are the two major reasons why there has been a major explosion in the human population size?
-The development of agriculture
-The development of manufacturing and trade which created the industrial revolution
Which factors may temporarily reduce the human population?