IB biology C4.1 populations and communities

define population

it is an interacting group of organisms of the same species living in an area that can interbreed

what is the main factor that distinguishes populations

reproductive isolation, or if organisms from the same species are not able to breed together successfully due to geographical, temporal, or behavioral isolation

what can lead to speciations

genetic variation that accumulates overtime and leads to speciation

what is the size of a population

the total number of individuals in it

why is it hard to count populations exactly

because some animals use camouflage, and they may be spread over a large area

what are estimates based on

sampling

what is s sample and why cant we only get one

they are small portions of something, and it is not representative of the whole population usually, so you get more to get a more accurate result

what is a random sample

it is one where every member has an equal chance of being selected to minimize bias and accurately reflect the overall population better

how do you estimate the population size of sessile organisms general

repeatedly placing a quadrat frame at random positions of a habitat and recording the number of organisms present at the time

how do you estimate the population size of sessile organisms exact

use a measuring tape to mark a base line along the edge of the habitat

generate random numbers

use the first random number for the distance along the measuring tape

use the second to measure the distance across the habitat at a right angle

place a quadrat precisely at that point

count the number of organisms in that spot. if they touch the line, go by whether a majority of the organism is in or out of the quadrat

repeat the experiment more times to ensure you get more samples

what is the equation for sampling sessile organisms

(number of organisms counted /number of quadrats) x number of quadrats

how do you estimate the population of mobile organisms exact

capture as many individuals as possible in the area

mark each captured individual

release all of the marked individuals and allow them to settle

recapture as many organisms as possible

calculate the population using the lincoln index

what is the equation for the lincoln index

(number of organisms caught and marked initiall x number of all individuals recaptured) / number of marked organisms recaptured, or MN/R

what are the assumptions of the lincoln index

the population is closed

mixing is complete, so the ratio of marked to unmarked is the same throughout

it is equally easy to catch all individuals

marks stay on the organism

what are the limitations of the lincoln index and capture mark release recapture method

capturing them may injure or stress them

marking them may make them more visible to predators

define density of a population

the number of individuals per unit area or volume

what happens around carrying capacity

the number of individuals in a population may fluctuate due to density independent factors, but the density-dependent factors tend to push it back towards the carrying capacity

what is top-down control

when organisms at higher trophic levels regulate the behavior of lower trophic levels in a food chain. It is mainly with predators, which exert control by consuming and limiting their prey

what is bottom-up control

the different resources that are available at lower levels and their overall amount influence the distribution of organisms at higher trophic levels, so things like nutrient availability and climate.

it affects oppositely

how does bottom-up control work with soil

it depends on the nutrients found in the soil, which influence the plants that can grow which influences the abundance of the herbivores and then later the predators and so on

it affects directly proportionally

what are two types of processes where chemical substances are released to deter potential competitors, and affect the dynamics of the ecosystem

allelopathy and antibiotic secretion

define allelopathy

it is the phenomenon in which one organism produces metabolites that influence the growth and success of other organisms

what are the two types of metabolites

primary metabolites: involved in normal growth

secondary metabolites: to impede or kill

what is an example of allelopathy in plants

sinigrin, which is used to inhibit other plant seed germination and reduce the root growth of plants growing in the area without affecting itself.

what is an example of allelopathy in microbes

penicillin which blocks bacterial enzymes involved in building cell walls and thus prevents the growth of bacteria arounfd the fungus, giving the bacteria a competitive advantage for food and for their own colonies to spread without others

what are density independent factors

factors that have the same effect no matter how large the population is such as natural disasters

what are density dependent factors

factors that have an increasing effect as the population becomes larger, and they are the basis for negative feedback mechanisms because they can help reduce large populations and regulate them, keeping them close to the carrying capacity like predation and the transfer of pathogens

what are the three groups of density-dependent factors

competition

predation

infectious disease

describe the predator prey relationships

usually there are less predators than prey

prey number will increase overtime before the predator population increases

food availability for the predators will increase

the predators will increase because they have low competition for food

the prey will decrease because they are being killed

the predator will reach a max because eventually the prey will be too low for the predator

can habitats accommodate an unlimited number of organisms

no, growth eventually stops or plateaus

what is carrying capacity

the maximum number of individuals that a particular habitat can support, which is represented by k

is carrying capacity a limiting factor and why

yes because it limits the survival of an organism

what do density dependent factors do

they keep the population at carrying capacity

why is reproduction positive feedback?

because it increases the number of individuals exponentially

what is the graph of a population size like usually

a sigmoid curve, changing from a J shape to an S shape from positive to negative feedback

what are the three phases of a population curve

phase 1: exponential phase

phase 2: transitional phase

phase 3: plateau phase

what happens in phase 1 of a population curve

there are many resources, low competition, favorable factors and low predation, so there is a lot of reproduction and a low death rate so there are more individuals increasing exponentially

what happens in phase 2 of a population curve

the density dependent factors cause the growth rate to slow down considerably due to negative feedback. there are more individuals so more competition, predators are attracted to greater food supply, and less distance between the organisms so diseases can spread easily

what happens in phase three of a population curve

the density dependent factors cause the size of the population to stay under the carrying capacity, stabilizing it and making the growth rate low or 0. there is less space for animals, more predators, limited supply for food, and the birth rate and immigration are equal to death rate and emigration

define community

a group of populations living together in an area and interacting with each other

define intraspecific relationship

one that exists between individuals of the same species usually within the same population

what is competition intraspecific relationship

it is when individuals in a population are members of the same species so they share an ecological niche and require the same resources. this leads to competition, and there will be natural selection over the generations for traits that allow individuals to compete more effectively

what is a cooperation intraspecific relationship

it is when individuals in a population cooperate together, helping one-another

what are some examples of cooperation intraspecific relationships

lions taking turns sleeping

wolves pack hunting

vampire bats caring for a neighbor’s baby

what is an example of competition intraspecific relationships

lizards competing for a place to lie

gorillas trying to mate

oak trees for sunlight

look at this

define herbivory

a feeding pattern where one animal is a herbivore and consumes plant materials as its primary source of nutrients like pandas

what is predation

an ecological interaction where a predator captures and consumes its prey like the bear

what is interspecific competition

it occurs when different species compete for limited resources within an ecosystem, which affects species distribution, abundance, and evolution of traits

what is parasitism

it is a type of symbiotic relationship where on organism, the parasite, benefits from its host like tapeworms

what is pathogenicity

it is when a pathogen invades and multiplies within the host’s tissues, disrupting the normal physiological functions and leading to various symptoms of illness like viruses like the retrovirus

what is mutualism

it is a symbiotic interaction between two or more species where both benefit from the relationship like bees and flowers

what is an example of mutualism in root nodules

legume plants which contain root fixing bacteria and play a vital role in converting atmospheric nitrogen into a usable form. the bacteria is provided compounds it needs for survival and the plant gets usable nitrogen

what is an example of mutualism in Orchidaceae

mycorrhizae fungi aid orchids by extending their hyphae into the soil, increasing the surface area for nutrient absorption

the fungi is then provided organic compounds from the orchid through photosynthesis

what is an example of mutualism in corals

zooxanthellae in hard corals live within the tissue of the coral and provide them with essential nutrients from photosynthesis that support coral growth, reproduction, and health. they also protect them from UV rays

the hard coral offer them a sheltered environment and access to sunlight for effective photosynthesis

what are the types of interspecific relationships

herbivory

pathogenicity

interspecific competition

predation

mutualism

parasitism

what is an example of invasive species

killer algae, which is not native to the Mediterranean sea but got there and it secretes a toxin that deters molluscs, herbivorous fish and sea urchins. it has no predators outside of its native range

in the Mediterranean sea, it had rapid growth, so it is leading to a decrease in biodiversity

what are endemic species

species that are only found in one place and nowhere else

what are invasive species

one that is non-native and when introduced to a new area it starts to cause problems for the species that are already living there. it is usually brought by humans

how do researches investigate the competition between two species

they selectively remove a species from the environment and observe the response of the other organisms. some species are successful, which shows interspecific competition. this is not definitive, but they can still look into patterns and make conclusions about the role of competition in the distribution and competition of species

what are the 3 general ways to investigate interspecific competition

field observation

field manipulation

laboratory experiments

what is the chi-squared test used for (test of independence)

to analyze if there is a significant association between two categorical variables , to see if there is an association in the presence of two species

what are the two hypothesis for a chi squared test

null: the distribution of species x and y are not associated

alternative: the distribution is associated (positive or negative)

what does the chi-squared test do and when is it valid

compares the observed quadrat sample values to expected values

it is only valid if all of the expected frequencies are 5+ and the sample was taken at random

how to do a chi-squared test

1-construct a contingency table where you plot observed values when x is present/absent and y is present/ absent and the total for each row and column

2-calculate the expected value by doing:

(row total x column total)/total

3-calculate the number of degrees of freedom:

(m-1)(n-1), where m is the number of rows and n is the number of columns

4-find the critical region, which is at a probability of 0.05

5-calculate the chi-squared value using:

x²= sum of (observed-expected)²/expected \

6- if x² is more than the critical value, the null hypotheses is rejected with 95% confidence. if it is equal or below, the null is accepted and there is no significant association between the two species detected

what are the limitations of the chi-squared test

it is very sensitive to sample size

can establish statistical association but not casual relationship