c4.1

Population

Population

Group or organisms of the same species interacting in a given geographical area

Within 1 species

Populations can show variations due to geographical or environmental factors

Reproductive isolation

The inability of organisms of the same species to successfully breed due to geographical isolation, behavioural isolation or temporal isolation (timing of mating)

Distinguishes populations and restricts gene flow between organisms, leading to accumulation of different genetic variations, can result in speciation

Why estimating population size is needed

estimation population size is needed for understanding of species dynamics, assessing ecological health, conservation strategies

Random sampling

Unbiased selection of organisms→ each individual has an equal chance of being chosen

representative sample → estimate accurately represents overall population

Quadrat sampling

Technique used to study populations of sessile species (fixed to one location)

-quadrat used, square frame of known area is randomly placed over a section of habitat recored, measure number of organisms of interest falling in quadrat recorded

-Randomly place over sections of the study area, using random generator and GPS
—observer counts and record the number of organisms in each quadrat

-estimation of population sizes

-analysis of spacial distribution patterns in a population

-If organism is half in the quadrat, researchers must establish a constant counting criterion

-data consistency, reliable data collection accurate estimations and analyses of populations

Another form of quadrat testing

-Capture images of habitat under study and overlay a grid on the photo

-each square represents a virtual quadrant of known area

-Useful for studying organisms difficult to access (In situ, method occurring in species natural habitat)

Sample appropriate number of quadrants across an area

habitats with high diversity or rare species may need more quadrants

mean number of organisms per quadrant is calculated by adding up counts and dividing by total number of sampled quadrants

mean value used to estimate population size

Estimating population size for motile organisms M x N/R

Capture- mark - release - recapture method

Capturing a significant sample of population

marking them in a way that does not harm their survival

release back into population

interact naturally in habitat

period of time passes

second sample collected

number of marked vs non marked individuals recorded

M= number of individuals captured and marked in first sample

N= Total number of individuals captured in second sample

R= Number of recaptured individuals already marked

Assumptions and limitations Lincoln method

-Marking technique has no influence on behaviour of organism

-Marked individual has same chance of being chosen and captured again as unmarked

-no birth death etc during study period

-studied individuals are representative of entire population

-Increased accuracy by increasing populations sizing and increasing repeats

Carrying capacity what is it and what is it influenced by

Maximum population size that a given environment can sustain over a period of time

influenced by availability of resources that play a role in determining number of individuals or species an ecosystem can support

Carrying capacity dynamic

Varies over space and time depending on abundance of limiting resources

not based on availability of one resource but by combination of limiting factors

when resources like food/water/space are limited, competition increases between everyone who needs it

Population density

Number of individuals per unit area or volume

how closely packed individuals are within a given space

size of population influenced by density dependent and independent limiting factors

Density dependent factors what are they and give examples

have a greater impact on population size as population density increases

factors are- competition for resources, predation, disease

increasing population, decreasing availability of resources, increasing competition

increasing competition, decreasing reproduction success rates, decreasing growth rates

Increasing population density, increasing spread of disease, increasing likelihood of predation, decreasing growth

Negative feedback mechanism

Density dependent factors act as negative feedback mechanisms, regulating population size, keep it closer to carrying capacity of environment

Fluctuation in population size helps retain relative balance in ecosystem, survival of both predator and prey species

Density independent factors

Impact on population regardless of its density

causes sudden and drastic changes

like floods, droughts, hurricanes

destroys habitats- effects survival rates of individuals

anthropogenic events like deforestation, urbanisation, pollution, climate change (human caused) disrupts population dynamics

impacts availability of resources, changing ecosystem carrying capacity

population exponential growth

J shaped curve, occurs in populations under ideal conditions when resources are unlimited, abiotic factors are favourable

Pattern normally seen in bacteria

Exponential growth in natural ecosystems

Limited by amount of nutrients, competition for resources, predation

prevents sustained exponential growth

expectation of unlimited resources and maximum reproductive capacity is unrealistic

Sigmoid growth in environments with limited resources

population first has exponential growth when resources are abudnant and low competition

when population keeps increasing, density dependent factors come into play, limiting rate of population growth, scarcity of resources leads to increase of competition and decreased growth rate

population reaches equilibrium at carrying capacity when birth rate= death rate

To graph population growth

Use logarithmic scale for y axis, population size, use non logarithmic scale on x axis time, scale logs compresses data, easier to observe patterns and trends

non logarithmic scale for time representation

Duckweed experiment

collect population growth data using yeast or duckweed, rapid growth under controlled experimental conditions

establish a population in a suitable growth medium, record population of yeast in suitable growth medium over time intervals

Intraspecific interactions

Interactions occurring between individuals of the same species

interactions competition and cooperation

Competition-

Male lions who compete for dominance and access of resources

population of birds, in competition for nesting sites and territories decreasing their breeding success and density

individuals of same species compete for limited resources leading to individuals adapting to special niches, displacement of less competitive individuals, regulation of population size

cooperation-

individuals collaborate to increase chances of survival and reproduction

-social amoeba which when they are starving , individual amoebas aggregate to form multicellular structure protects and allows them to obtain and share nutrients

-In a bee colony, bees work together in a highly organised manner, each with a specific job

Communities

diverse array of populations within a specific area ranging from plants, animals, fungi, bacteria

Interspecific interactions

Relationships that occur between different species within an ecosystem

ecological interactions below

Herbivory

Fundamental feeding relationship when a herbivore consumes plant material as its primary nutrient source

occurs with the giant panda and bamboo plants

giant panda adapted to feed exclusively on bamboo, relying on its nutrient value

evolved specialised traits to effectively extract nutrients from plants

Predation

Predator captures and consumes its prey

grizzly bears and salmon

grizzly bears as predators rely on salmon prey for a source of energy

predation shapes behaviour, population size, reproductive success of salmon

Interspecific competition

Different species compete for limited resources within an ecosystem

implications on species distribution, abundance, evolution of traits due to acquiring resources

Eastern Grey squirrels and American red squirrels in North America

Compete for similar food resources, affects growth and survival of populations

Parasitism

Symbiotic interaction when one organism, the parasite, benefits at expense of its host

parasite lives on or within the host taking nutrients and resources leading to harm

tapeworms live in the intestines of host organisms, absorbing nutrients from they digestive systems

evolved adaptations to exploit hosts while minimising damage causing death

Pathogenicity

Pathogen is a micro-organism like a virus, bacteria, or fungus capable of causing disease in its host

Invade and multiply within host’s tissue and disrupt physiological functions

Direct and immediate detrimental effect on host

spread easily host to host

influenza viruses

Mutualism

Symbiotic interaction (between two different organisms) here both parties obtain benefits from the relationship

root nodules in Fabaceae mutualism

root nodules in Fabaceae-

Legume plants in the fabacecae family

contain root nodules filled with nitrogen fixing bacteria which convert atmospheric nitrogen into a usable form

bacteria provide legume with nitrogen, plants provide bacteria with carbohydrates/compounds for growth and survival

Mycorrhizae in Orchidaceae

mycorrhizae in Orchidaceae-

specialised mycorrhizae fungi colonise orchid roots

fungi aid orchids with getting nutrients by extending their hyphae into soil, increasing surface area for nutrient absorption

orchids provide fungi with organisms compounds produced through photosynthesis

Zooxanthellae in hard corals

-Photosynthetic algae called zooxanthella live in tissues of hard corals

-provide coral with essential nutrients from photosynthesis that help coral growth and reproduction

-provide coral with vibrant pigment to protect them from excessive UV radiation

-coral offers a sheltered environment and access to sunlight for photosynthesis

Invasive species

-introduced to new environments where conditions are favourable for them to rapidly establish and spread unlike native species

highly effective use of resources

leads to rapid decline or extinction of endemic species (naturally found in specific region)

competitive advantage in resource acquisition over endemic species

Invasive species killer algae

killer algae native to indian ocean introduced to Mediterranean sea

algae secretes a toxin that deters molluscs, herbivorous fish, sea urchins

lacks natural predators outside its native range

in its new habitat it competes with native marine plants forming dense mats

smother and displace native species

rapid growth and absence of predators

allows it to spread and lower native biodiversity

Testing interspecific competition

To assess the impact of a species remove it from the community

researchers can closely observe responses of remaining organisms- shows impact of competition on distribution and success

success of another species in absence of one can show interspecific competition

correlation does not offer definitive proof

can use laboratory experiments to provide controlled conditions, then manipulate a variable to show effect on success of species

can use field observations using random sampling, allowing researches to get data on species abundance and distribution, can show potential competition

Chi squared test which tests can we use

Determine whether there is a significant association between 2 categorial variables

association between presence of 2 species?

does the relationship between 2 species occur due to chance?

test of independence

use quadrant sampling- 2 species are associated with each other they will be found within the same quadrants

negative association arise due to competition for same limited resources (interspecific competition)

steps of chi squared test

2 hypothesis established

-null hypothesis: distribution of species X and Y is not associated

-alternative hypothesis: distribution of species X and Y is not associated

test only valid if frequency Is five or larger and sample is taken randomly from population

use a contingency table to input observed values

do expected frequency = row totalxcolumn total/ grand total

calculate degrees of freedom- (number of rows in the table-1)( number of columns - 1 )

Using degrees of freedom plug in table and determine critical region like 0.05 (p) probability, look what its value is for your degrees of freedom (critical values)

calculate X² = sum of (O-E)²/E

o= observed frequency e= expected

compare this value with the critical value, if it is higher than the critical value we can reject null hypothesis and accept alternative, if it is lower we can reject alternative and accept all

limitations chi squared test

Must have a large sample size but not too large to where it takes forever

can only determine a statistical association not a casual relationship

doesnt account for outside factors influencing results

control of populations

regulation of size and growth of populations in an ecosystem

maintain balance and prevent detrimental effects like resource depletion and overexploitation

Density dependent control

Predators play a role in regulating prey populations

predator- prey relationships are an example of animal populations being regulated by density dependent factors and negative feedback

predator populations increases, increased predation, increased pressure on prey, decrease in prey numbers, decrease in food availability for predators and decrease in predator numbers- fluctuation cycle of population regulation

ex. interaction between cheetahs and gazelles

increased population of gazelles, increased food availability for cheetahs, increased population of cheetahs, increased predation pressure on gazelles, decrease in gazelle population, decrease in food supply for cheetahs, decreased cheetah population

top down control

abundance/behaviour of lower trophic levels in a food chain is regulated by presence and activities of organisms at higher levels

consuming and limiting abundance of their prey; predators shape structure and dynamic of lower trophic levels

bottom up control

availability of resources at lower trophic levels influences abundance and distribution of organisms at higher trophic levels

factors like nutrient availibility, climatic conditions, primary productivity, exert bottom up control

in a terrestrial ecosystem, avialibilty of soil nutrients determine growth of plants and the abundance of herbivores that rely on them for food

both of these are possible, but one is more likely to be dominant in a community

allelopathy and antibiotic secretion

2 processes in which organisms release chemical substances into their environment to deter competitors

example allelopathy

black walnut tree, releases a chemical compound called juglone into soil, acting as a potent inhibitor, suppressing growth of nearby plants, inhibits key physiological processes in competing plants, creates zone of reduced plant diversity around it

example antibiotic secretion

streptomyces bacteria; found in soil/marine environment, ability to synthesise range of antibiotics like streptomycin acting as a defence mechanism giving it a competitive advantage

can be used as medicine to treat bacterial infections as it acts as a defence