POPULATIONS AND COMMUNTIES (C4.1)

What is a population?

Refers to a group of organisms of the same species that typically interbreed, sharing a common gene pool

What is a key factor that distinguishes populations?

Reproductive isolation: the inability of organisms of the same species to successfully breed due to geographical isolation, behavioural isolation, or temporal isolation

• These barriers restrict gene flow between organisms, leading to accumulation of different genetic variations and the creation of distinct populations

Why would one use random sampling to measure population size, and how?

• Random sampling involves the unbiased selection or organisms, where each individual has an equal chance of being chosen

• By randomly selecting individuals, scientists can minimise bias and obtain a representative sample

• Researchers decide the fores area into smaller more manageable sections (grid), and randomly select parts fo the grid

What is sampling error?

Refers to the discrepancy between our estimated value and the true value of the population size

• This is always seen when using random sampling method

What is quadrat sampling?

Technique to study populations of sessile organism, like plants and corals .

• Involves placing a square frame (quadrat) of known area randomly within a study site.

How does one conduct quadrat sampling?

• Randomly place multiple quadrats in the habitat.

• Count the number of target organisms within each quadrat.

• Use a consistent counting rule (e.g., include organisms if more than half falls within the quadrat).

• Use at least 10 quadrats for reliability

How does one estimate the population size of motile/ moving organisms?

• Capture- mark- release- recapture

• Lincoln index

What is the capture-mark- release- recapture method?

• Capturing a significant sample of the population and marking them in a way that does not harm the survival of organisms.

• Organism are then released back into the population, allowing them to interact with unmarked individuals

• After some time, second sample is collected, and number of marked vs unmarked are recorded

• Using the data, use Lincoln index to estimate population size

What is the formula for the Lincoln index?

M x N/R

• M = number of individuals captured and marked in the first sample

• N = total number of individuals captured in the second sample

• R= number of recaptured individuals that were already marked

What are limitations to the capture-mark-release-recapture method?

• Assumes that the marking does not have any infleuce on behaviour or survival of organism

• Assumes marked individuals full reintegrate into the population. and have equal chances of being captures compared to unmarked individuals

• Assumes there are no births, death, immigrations or emigration during study period

What are limitations to the Lincoln index?

• Relies on the assumption that the marked individuals used are representative of entire population

• Assumes ration of marked to unmarked in second sample reflects the ratio of the population

What does the carrying capacity of an organism mean?

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

• Influenced by the availability of resources determining the number of individuals that an ecosystem can support

  • Food

  • Water

  • Fossil Fuels (now)

  • Soace

What is interspecific competition?

Competition occurring between members of different species

What is intraspecific competition?

Competition happening among members of the same species

What is population density?

The number of individuals per unit area or volume

• Provides a measure of how closely packed individuals are within a given space

What are density-dependent factors?

• Greater impact on population size as the population density increases.

  • Competition for resources

  • Predation

  • Disease

  • Parasitism

• This competition can result in reduced reproductive success, decreased growth rates and increased mortality.

• Act as negative feedback mechanisms that help regulate and control population size, keeping it closer to the carrying capacity of the environment

What are density-independent factors?

• Affect population size regardless of density.

• Examples: natural disasters (floods, droughts, hurricanes, earthquakes).

• Human-induced (anthropogenic) examples: deforestation, urbanisation, pollution, climate change.

• Can change resource availability and ecosystem carrying capacity.

What is exponential population growth?

• Occurs under ideal conditions with unlimited resources.

• Represented by a J-shaped curve.

• Common in lab-grown bacterial populations.

• Not sustainable in natural ecosystems due to limiting factors.

What is the sigmoid population growth?

• Occurs when resources are limited.

• Represented by an S-shaped curve.

• Growth slows as population approaches carrying capacity.

• Example: Wolves on Isle Royale—initial rapid growth, then stabilisation due to predator-prey interactions with moose.

What are 2 categories of a intraspecific relationship?

• Competition

• Cooperation

What is competition in relation to intraspecific relationships? Examples?

• As members of the same ecological niche require the same resources, and unless the resource is abundant, there is competition

• More successful individuals gain the sources

• Leads to natural selection

• EG:

  • duckweed competes for light when crowded

  • gannets compete for nest sites on sea cliffs

What is cooperation in relation to intraspecific relationships? Examples?

• Individuals in a population may cooperate in a variety of ways.The extent of cooperation varies, with most in social animals such as termites.

• EG:

  • chimpanzees hunt ni groups, increasing the chance of catching monkeys or other prey

  • mackerel swim in tightly packed, fast-moving "bait balls" making it harder for predators to catch them

What are the relationships between species not living in close association?

• Herbivory

  • Bison feeding on grasses

• Predation

  • Anteaters feeding on ants

• Interspecifc competition

  • Ivy competing with oaks

What are the relationships between species living in close association?

• Mutualism: 2 species live in close association with both species benefiting from the association

  • Zooxanthellae in hard corals

• Pathogenicity: One species (the pathogen) lives inside another species (the host)and causes a disease in the host.

  • Antrax bacteria in kudu

• Parasitism : One species lives in or on another species and obtains food from them. The host is harmed and parasite benefits

  • Black-legged ticks on white-tailed deer

What are invasive species and why do they pose a threat for the balance of ecosystems worldwide?

An organism that is not indigenous, or native, to a particular area and can potentially cause harm to the ecosystem

• Due to their efficient use of resources, invasive species can lead to the rapid decline and even extinction of endemic species

What is an example of invasive species?

• Killer algae was introduced into the Mediterranean sea from the Indian ocean

• They secrete toxin that deters molluscs, herbivores fish and seas urchins, and lack natural predators outside its native range

• In this new habitat, it competes with native marin plants by forming dense mats that smother and displace native spices

• Its rapid grwoth and absence of predators allows it to spread unchecked

How can one test for interspecific competition?

• Laboratory experiments

  • controlled settings where variables can be manipulated

• Field observations

  • Random sampling

• Field manipulations by species removal

What does chi-squared test provide?

Evidence for interspecific competition

How is predator–prey relationships an example of density-dependent control of animal populations?

• Cheetahs and gazelles

  • When population of gazelles increases, it provides lots of food for cheetahs, leading to rise in cheetah population

  • As cheetah numbers grow, the increased predation pressure causes a decline in the gazelle population due to higher rates of predation

  • The reduction in gazelle numbers ultimately impacts the cheetah population as their food supply

When does top down control occur?

Occurs when the abundance or behaviour of lower trophic levels in a food chain is regulated by the presence and activities of organisms at higher trophic levels.

When does bottom up control occur?

Occurs when the availability of resources at lower trophic levels influences the abundance and distribution of organisms at higher trophic levels.

What is allelophaty and give an example of it?

• Process in which organisms release chemical substances into their environment to deter potential competitors

• EG:

  • Black walnut tress release chemical compound juglone, which acts as a potent inhibitors, suppressing the growth of nearby plants

What is antibiotic secretion and give an example of it?

• Process in which organisms release chemical substances into their environment to deter potential competitors

• EG:

  • Streptomycin bacteria found in soil have ability to synthesise a wide range of antibiotics, and they act as a defence mechanism