C4.1 populations and communities (year 6) Flashcards
Describe 3 methods of population estimation
Systemic sampling:
- a line or grid is set up and measurements/counting are carried out only at specific intervals
Random sampling:
- suitable for sessile (stay in one place) animals/plants
- arbitrairly chosen zones of the populations geographic zone are sampled
- random distances/directions are used to overcome any bias
Lincoln index:
- suitable for motile organisms
- capture-mark-release-recapture method
- upon recapture, some organisms are marked and unmarked.
- total population = M x N/R where
M = no. of individuals originally caught and marked, N = total no. of indiv recaptured, R = no. of marked indiv recaptured
- this method risks injuring organisms, and assumes that the population is closed with no immigration/emigration
Definition of carrying capacity
The maximum no. of organisms a habitat can support
- represented by K
Describe how population size is controlled by -ve feedback and density-dependent factors
+ve feedback is not used as it could lead to food shortages, spread of disease etc
-ve feedback prevents a system from going too far in one direction. e.g. if a population grows uncontrollably, the resources such as space, food, water will start to run out.
- the chances of disease spreading/predators to an area increase as population increases.
- there is also increased competition of resources
- all of this ensures that the habitat does not go past its carrying capacity
Describe the sigmoid curve that represents the stages of population growth
(s-shaped graph)
Exponential:
- plentiful resources, little to none competition/predation/disease
- favourable abiotic conditions (temp, light)
Transitional:
- with population increasing, competition increases
- more predators attracted
- disease opportunity increase
Plateau:
- predators and disease increase mortality, growth curve levels off
- no. of births/immigrations balanced by no. of deaths
- limited food supply = smaler no. of offspring, emigration to places w more abundant food
Describe cooperation/competition in intraspecific r/s + examples
Intraspecific cooperation:
- indiv of a species helps another indiv from the same species to ensure the survival of the group
- e.g. hunting as a pack like wolves = higher chance of success
- e.g. caring for anothers young like vampire bats while the mother is looking for food
Intraspecific competition:
- indiv of a species compete for the same resources
- e.g. competing for space/sunlight as oak trees, zones of grazing pasture for bison
Describe the 6 types of interspecific interactions + examples for each one :)
Herbivory - eating plant material e.g. snails eating leaves
Predation - killing and eating prey/smth that recently died e.g. lions hunting zebra
Interspecific competition - 2 species for the same resource e.g. oak vs fir tree for sunlight/space
Mutualism - 2 species providing resources for mutual benefit e.g. Lichens are made up of an alga providing food using photosynthesis and a fungus providing minerals
Parasitism: 1 species living on/in and depending on another for food/part of its life cycle. Host is not harmed by parasite e.g. Parasites belonging to the genus Plasmodium cause malaria in humans, reproducing in the liver and RBC
Pathogenicity: ability of microbes such as bacteria/viruses to cause disease in another species e.g. Pneumonia is a transmissible disease caused by a pathogen.
describe 3 examples of mutualism
Rood nodules in legume family:
- Rhizobium bacteria live in the root nodules of plants in the legume family, converting nitrogen gas from the air to ammonia
- ammonia acts as a fertilizer for plants, and the Rhizobium bacteria receive carbohydrates and a favourable environment in the nodules of their host plant.
Mycorrhiza:
- a plant and a fungus help each other
- e.g. species of orchids rely on fungi to provide energy and nutrients for germination.
- Some plants are non-photosynthetic and are heterotrophs, relying on fungi to decompose dead material and pass nutreints to them via a root-like system of hyphae. The fungi benefit from the nutrients released as they decompose the dead orchids
Zooxanthellae in hard corals:
- Zooxanthellae can photosynthesize and form a symbiotic r/s with coral polyps, giving them food in the form of carbon-based energy molecules made from sunlight. In exchange, the coral polyps give CO2 and minerals, which are needed for photosynthesise and growth, also providing a home
Endemic vs invasive species
Endemic: species if only found in a specific area and nowhere else
Invasive: introduced into a new area from a distant origin and their populations grow so well that they start to cause problems for the species that are living there
Describe tests for interspecific competition
Interspecific competition is indicated but not proven if one species is more successful in the absence of another.
- laboratory experiments
- field observations (random sampling)
- field manipulation (removal of a species)
- a PRESENCE-ABSENCE matrix is used at the end of a study where presence is recorded as 1 and absence is 0.
Describe + 1 example of predatory-prey r/s as an example of density-dependent control of animal populations
As organisms rely on each other, it would be a disadvantage for one species in a community to completely take over.
e.g. is a rabbit population increased by too much, food supply would become more and more scarce, more predators attracted, higher chance of disease spreading.
- so, predators provide a form of population control as their activity increases as a population of prey increases. e.g. the CANADA LYNX and SNOWSHOE HARE where the predator population reaches its maximum after the prey popuation.
What are top-down and bottom-up controls
Limiting factors can be top-down or bottom-up
Top-down:
- species population reduced by other species feeding on it.
Bottom-up:
- species population reduced by a lack of resources such as food, sunlight, minerals
diff btwn primary and secondary metabolites
Primary: moelcules needed for the basic functions of life e.g. energy and growth
Secondary:
- molecules needed to impede or kill competitors e.g. molecules involved in allelopathy, the production of secondary metabolites that influence the growth and success of other organisms
Example of alleopathy in plants
GARLIC MUSTARD:
- produces a secondary metabolite called SINIGRIN
- sinigrin inhibits the germination of seeds from other plants
- reduces the growth of roots of plants already growing in the area
- gives garlic mustard a competitive advantage over other plants
Example of allelopathy in microbes
PENICILLIUM RUBENS:
- single-celled fungus produces PENICILLIN, which stops the growth of bacteria.
- penicillin is an antibiotic
- allows P.rubens to compete for space and food sources to establish a bacteria-free zone around them
