IB Biology HL: Populations & Communities (C2.1) and Transfers of Energy & Matter (C4.2)

Population

• A group of individuals of the same species living in the same area and capable of interbreeding

Pre-Zygotic Barriers

• Barriers that prevent mating our fertilization from occurring in the first place

Habitat Isolation 

• Populations live in different habitats and rarely encounter each other. 

Temporal Isolation

• Populations breed during different times of the day or year.

Behavioral Isolation

• Different courtship rituals or mating behaviors prevent recognition between individuals.

Mechanical Isolation

• Structural differences in reproductive organs prevent successful mating.

Gametic Isolation

• Sperm and egg are incompatible, preventing fertilization.

Post-Zygotic Barriers

• These barriers occur after fertilization, but the resulting hybrid offspring are either inviable (do not survive) or infertile (cannot reproduce). 

Reduced Hybrid Viability

• Hybrid offspring may not survive.

Reduced Hybrid Fertility

• Even if hybrid offspring survive, they may be infertile.

Hybrid Breakdown

• First-generation hybrids may be fertile, but subsequent generations may not be.

Sample

• A small part or quantity intended to show what the whole is like

What are the purposes of sampling a population? List 3 reasons

1. Time: There is not enough time to count all individuals in ecosystems, so sampling allows scientists to determine reasonably accurate estimates.

2. Destructive Sampling: Collecting data may involve damage to the habitat. Sampling reduces the impact on the environment.

3. Feasibility of Counting: Many animals move in and out of ecosystems, therefore a count cannot be accurate. Sampling allows scientists to determine estimates of species present at different times.

Sampling Error

An error in a statistical analysis arising from the unrepresentativness of the sample taken.

Why is there a need for randomness in sampling procedures? List 3 reasons

1. Representations: It is important that all individuals in a location could possibly be selected for sampling 

2. Removal of biases: Random sampling emoves biases when selecting locations to collect data 

3. Generalization: Random sampling allows scientists to generalize data from samples to a larger habitat

Quadrat Sampling

• Sampling method for sessile (stationary) organisms

• Used to estimate population size by randomly placing square frames (quadrats) in an area and recording the organisms within them

Capture-Mark-Release-Recapture Method

• Sampling method for motile (mobile) organisms

• Used to estimate population size, involving capturing, marking, releasing, and then recapturing individuals

How can you use quadrat sampling to estimate the population of a sessile organism?

1. Randomly place quadrats (square frames) in the study area

2. Count the number of individuals within each quadrat,

3. Extrapolate these counts to estimate the overall population size. 

How can you use the capture-mark-release-recapture sampling method to estimate the population of motile organisms?

1. Capture a number of individuals using nets, traps, or other methods

2. Mark them using non-toxic paint in a way that won't make them more visible to predators

3. Release the marked individuals (M) and wait some time for them to mix with the population

4. Perform a second round of capture and count the total number captured (N) and the number that have marks (R)

• The population can be estimated with the formula (called the Lincoln index): Population size = (M x N)/R

What are the assumptions made about a population when using the mark-recapture method of estimating a population? List 6 assumptions

• Closed Population:The population is assumed to be closed, meaning there's no immigration (individuals entering the study area) or emigration (individuals leaving). 

• No Births or Deaths: The population size is assumed to remain relatively constant between the marking and recapture periods, meaning there are no significant births or deaths. 

• Random Mixing: Marked individuals are assumed to mix randomly with the unmarked individuals in the population, ensuring that all individuals have an equal chance of being captured. 

• No Effect of Marking: The marking process itself is assumed to have no effect on the individuals' behavior, survival, or likelihood of being recaptured. 

• Marks are Permanent and Not Lost: The marks used to identify individuals are assumed to be permanent and not lost or faded between the marking and recapture periods. 

• Equal Catchability: Each individual in the population has an equal and independent chance of being captured.

Lincoln Index

Carrying Capacity

• The maximum number or organisms in a population that an ecosystem can support

What are some examples of resources that can limit the carrying capacity of a population? List 7 examples

1. Availability of Food 

2. Availability of Water 

3. Space 

4. Shelter 

5. Diseases 

6. Predators 

7. Climate 

How is populations size an example of a negative feedback loop?

• As a population grows, resource scarcity and competition increase, leading to a decline in the population's growth rate, thus stabilizing the system.

Density-Dependent Factors

• These factors have a greater impact on a population as its density (number of individuals per unit area) increases.

• They can act as a natural check on population growth, preventing it from exceeding the carrying capacity of the environment.

Density-Independent Factors

• These factors affect a population regardless of its density, meaning their impact is the same whether the population is large or small. 

• They can cause sudden and dramatic changes in population size, often leading to population crashes.

What are some examples of density-dependent factors that maintain a population carrying capacity? List 5 examples

1. Competition: As a population grows denser, individuals compete more intensely for limited resources like food, water, shelter, and mates, leading to reduced survival and reproduction. 

2. Predation: Higher prey densities can attract more predators, increasing mortality rates within the prey population. 

3. Disease: Diseases spread more rapidly in dense populations, leading to higher mortality rates. 

4. Resource Depletion: As a population grows, resources like food, water, and space become scarcer, leading to increased competition and reduced survival. 

5. Waste Accumulation: Dense populations can lead to the accumulation of toxic waste products, negatively impacting survival and reproduction.

What are some examples of density-independent factors that help maintain a population's carrying capacity? List 3 examples

1. Natural Disasters

2. Extreme Weather Events:

3. Pollution

Explain the ability of species to reproduce more offspring than the environment can support.

• Species have the capacity to produce far more offspring than their environment can sustain which leads to competition for resources and the "struggle for existence" where only some survive to reproduce. 

What are some examples of conditions in which populations can grow exponentially? List 6 examples

1. Unlimited Resources: Abundant food, water, space, and other necessities allow for continuous reproduction and survival, promoting rapid population growth. 

2. Favorable Environmental Conditions: Ideal temperatures, suitable shelter, and minimal competition or stress factors enhance reproductive rates and survival. 

3. Low Initial Population Density: When a population starts small, resources are more readily available, and the growth rate can be initially very high. 

4. Minimal Predation and Disease: Reduced mortality rates due to fewer predators or diseases allow more individuals to survive and reproduce, accelerating population growth. 

5. High Reproductive Rate: Species with fast reproduction rates, like bacteria, can exhibit more pronounced exponential growth. 

6. Ecological Vacuum: A situation where a species is not limited by other species (no predation, parasitism, or competitors) and resources are not limited, and the environment is constant.

What are the reasons for the pattern of a sigmoid population growth curve? List 4 reasons

1. Resource Availability: The availability of food, water, space, and other resources directly impacts the population's growth rate. 

2. Competition: As the population size increases, competition for resources intensifies, leading to a decline in the growth rate. 

3. Predation and Disease: Predation and disease can also limit population growth, particularly as the population density increases.

4. Carrying Capacity (K): The maximum population size that an environment can sustain is known as the carrying capacity (K). The sigmoid curve shows how a population approaches and stabilizes around this carrying capacity.

Sigmoid Exponential Growth Curve

What are the 4 different phases of a sigmoid exponeneteial growth curve?

1. Lag Phase: In the initial phase, the population size is small, and resources are abundant, leading to slow growth as the population adapts to the environment.

2. Exponential Growth Phase: As resources become more abundant and the population grows, the growth rate accelerates, resulting in a rapid increase in population size.

3. Transition Phase: As the population continues to grow, resources become limited, and competition intensifies, causing the growth rate to slow down.

4. Stationary Phase: The population size stabilizes, with the birth rate roughly equal to the death rate, as the population reaches the environment's carrying capacity (K). This is the point where the curve flattens out.

Why should you use a logarithmic scale when plotting change of a population over time?

•  Vvisualize data with a wide range of values, making it easier to understand the rate of change and detect shifts in growth patterns, especially when dealing with exponential growth

What is a method for monitoring the population of yeast or duckweed over time?

• Grow in petri-dishes or beakers filled with water.

How can you use data of yeast or duckweed population over time to compare observed and expected population growth curve?

• Collect data on their population size over time

• Model the expected growth using a mathematical equation (like exponential or logistic growth)

• Compare the model's predictions to the observed data through graphing

Intraspecific Relationship

• Interactions that occur between individuals of the same species

What is the cause and effect of competition in a population?

• Competition (from limited resources) drives population dynamics which leads to effects like reduced growth, reproduction, and potential population decline and Influencing evolutionary adaptations and community stability. 

What is the cause and effect of cooperation in a population?

• Cooperation is driven by factors like resource scarcity or environmental pressures, which leads to increased survival and reproductive success for individuals and the overall population.

What are some examples of competition in plants and animal populations? List examples for interspecific and intraspecific

• Interspecific Competition:

  • Plants: Different plant species in a forest might compete for sunlight, water, and nutrients in the soil. For example, taller trees shade out smaller plants, limiting their growth. 

  • Animals: Lions and cheetahs in the African savanna both prey on zebras, antelopes, gazelles, and wildebeest, leading to competition for food resources. 

• Intraspecific Competition:

  • Plants: Within a plant population, individuals might compete for resources like sunlight, water, and nutrients, leading to stronger individuals outcompeting weaker ones. 

  • Animals: Male deer competing for mates during the rut is an example of intraspecific competition, where the strongest males secure breeding opportunities. 

What are some examples of cooperation in plants and animal populations? List 4 examples

• Mutualism:

  • Plants: Some plants engage in mutualistic relationships with fungi, where the fungi help the plant absorb nutrients from the soil, while the plant provides the fungi with sugars. 

  • Animals: Clownfish and sea anemones exhibit a symbiotic relationship, where the clownfish find shelter within the anemone's tentacles, and the anemone benefits from the clownfish attracting prey. 

• Cooperative Hunting:

  • Animals: Lions hunt in packs, coordinating their efforts to bring down large prey, increasing their hunting success. 

• Cooperative Breeding:

  • Animals: In some bird species, multiple individuals help raise the young, sharing the responsibility of feeding and protecting the chicks. 

• Cooperation in Defense:

  • Animals: Ostriches and zebras sometimes form mixed-species herds, where they can alert each other to danger, increasing their chances of survival. 

Community

• The group of all populations living in the same area and interacting with one another

What is an example of a community or organisms?

• A coral reef is a complex community with many interactions between populations.

• Most corals have photosynthetic unicellular algae called zooxanthellae living inside their cells.

Mutualism

• A symbiotic relationship where both species benefit from the interaction.

What are some examples of mutualism?

• Lichens, a symbiotic relationship between fungi and algae/cyanobacteria, where the fungus provides structure and the algae/cyanobacteria photosynthesize, benefiting both.

• Termites and protozoa, where termites benefit from the protozoa's ability to digest cellulose, and the protozoa benefit from a protected environment and food source.

• Pollination, where plants benefit from the transfer of pollen by animals, and the animals benefit from nectar or pollen as food.

• Mycorrhizal fungi and plant roots, where fungi help plants absorb nutrients, and the plants provide sugars to the fungi. 

Competition

• A relationship where two or more species compete for the same limited resources, such as food, water, space, or mates.

What are some examples of competition?

• Two species of birds competing for the same type of seeds in a limited area.

• Different plant species competing for sunlight and water in a forest.

• Two species of bacteria competing for nutrients in a petri dish. 

Predation

• A relationship where one species (the predator) kills and consumes another species (the prey).

What are some examples of predation?

• A lion hunting and eating an antelope.

• A spider catching and eating an insect.

• A hawk preying on a mouse.

Herbivory

• A type of predation where an organism (the herbivore) consumes plants or other autotrophs.

What are some examples of herbivory?

• A cow grazing on grass.

• A caterpillar eating leaves.

• A deer browsing on twigs. 

Parasitims / Pathogeneic Interactions

• A relationship where one species (the parasite or pathogen) benefits at the expense of another species (the host).

What are examples of parasitism and pathogenic interactions?

• Parasitism:

  • A tick feeding on the blood of a dog.

  • A tapeworm living in the intestines of a human.

  • A parasitic plant, like mistletoe, growing on a tree.

• Pathogenic Interactions:

  • A bacterium causing an infection in a human.

  • A virus causing a disease in a plant.

  • A fungus causing a disease in an animal.

What is the mutualistic relationship within root nodules in Fabaceae (legume family)?

• In the mutualistic relationship within root nodules of Fabaceae (legume family), nitrogen-fixing bacteria (rhizobia) convert atmospheric nitrogen into a usable form for the plant (ammonia), while the plant provides the bacteria with sugars and other nutrients.   

What is the mutualistic relationship within mycorrhizae in Orchidaceae (orchid family)?

• Orchid mycorrhizae are a crucial mutualistic relationship where orchids rely on specific fungi for nutrient acquisition, especially during early development, in exchange for providing the fungi with carbohydrates, a relationship vital for orchid germination, growth, and survival. 

What is the mutualistic relationship of zooxanthellae in hard corals?

• Hard corals and zooxanthellae, a type of algae, have a mutualistic relationship where the coral provides a protected environment and nutrients, while the zooxanthellae provide the coral with food (carbohydrates) and oxygen through photosynthesis.

Endemic Species

• Unique to a specific geographic area, meaning they are found naturally only in that particular region and nowhere else in the world. 

Invasive Species

• Non-native organisms (plants, animals, or other organisms) that are introduced to an ecosystem and cause harm to the environment, economy, or human health.

What is the effect of invasive species on the realized niche of an endemic species?

• Invasive species can significantly reduce the realized niche of an endemic species by out-competing them for resources, directly preying on them, or altering the environment, leading to a smaller area or range where the endemic species can survive and thrive. 

How is competition for resources an example of endemic and invasive species?

• In the Great Lakes region, invasive Asian carp compete with native fish for resources like food (plankton) and habitat, potentially leading to the decline of native fish populations and disrupting the ecosystem.

What is the methodology and limitation of using a chi-squared test to asses the presence of interspecific competition in a community?

• A chi-square test can assess interspecific competition by examining if the distributions of two species are independent, rejecting the null hypothesis of independence if a significant association is found, potentially indicating competition or other interactions.

• Doesn't distinguish between competition and other factors, and its limitations include requiring large sample sizes and independent data. 

How can you use direct experimentation to assess the presence of interspecific competition in a community?

• Direct experimentation, like removing or manipulating species, is used to assess interspecific competition by observing how the presence or absence of a species affects the population dynamics and resource use of other species in a community, thereby revealing whether competition is occurring

What is the null hypothesis of a chi-squared test of association between species in a community?

• Null Hypothesis (H0): The species distributions are independent, meaning the presence or absence of one species does not influence the presence or absence of another. 

  • (Accept if P > 5% )

What is the alternative hypothesis of a chi-squared test of association between species in a community?

• Alternative Hypothesis (Ha): The species distributions are not independent, suggesting there is a relationship (positive or negative) between their occurrences.

  •  (Accept if P < 5%)

How do you use a contingency table to complete a chi-squared test of association between species in a community?

• Organize data into a table showing observed frequencies

• Calculate expected frequencies assuming independence,

• Compare observed and expected values using the chi-square formula.

What is the typical dynamic equilibrium of populations of predator and prey?

• In a predator-prey relationship, populations fluctuate in a cyclical manner, with predator populations increasing as prey becomes more abundant, and then decreasing as prey numbers decline, leading to a dynamic equilibrium where neither population can grow unchecked. 

What is an example of an oscillating cycle of predator and prey population sizes?

• A classic example of an oscillating predator-prey cycle is the relationship between the snowshoe hare (prey) and the Canada lynx (predator), where their populations fluctuate in a cyclical pattern, with hare populations peaking before lynx populations.

Top-Down Control of Populations

• The influence of predators or higher trophic levels on the populations of lower trophic levels (prey).

• For example, if a predator population increases, it can lead to a decrease in the population of its prey, which can then have cascading effects on the entire food web. 

Bottom-Up Control of Populations

• The abundance of resources or lower trophic levels (like plants or primary producers) influences the populations of higher trophic levels.

• For instance, if there's an increase in nutrient availability, it can lead to an increase in plant biomass, which in turn can support larger populations of herbivores and, subsequently, carnivores. 

Allelopathy

• A biological phenomenon where one organism, often a plant, produces chemicals (allelochemicals) that influence the growth, survival, and reproduction of other organisms, either beneficial or detrimental.

What is an example of allelopathy?

• A prime example of allelopathy is the black walnut tree (Juglans nigra), which releases the chemical juglone, toxic to many plant species, from its roots, leaves, and nut hulls, inhibiting the growth of nearby plants like tomatoes and azaleas.

Antibiotics

Substances that inhibit or kill bacteria

What is an example of the actual production and function of antibiotics?

• An example of natural antibiotic production and function is the Streptomyces bacteria, which produce the antibiotic streptomycin that inhibits bacterial cell wall synthesis, thus preventing bacterial growth and killing them.

Ecosystem

• A community of interacting living organisms (biotic factors) and their non-living environment (abiotic factors) functioning as a unit.

Open System

• Allows the exchange of both matter and energy with its surroundings

• (Example: Ecosystems)

Closed System

• Allows the exchange of both matter and energy with its surroundings

• (Example: Ecosystems)

Explain how ecosystems are open systems

• Ecosystems are considered open systems because they continuously exchange both energy and matter with their surroundings, unlike closed systems which do not exchange either.

Explain how sunlight is the primary energy source for most ecosystems

• Sunlight is the primary energy source for most ecosystems, as it fuels photosynthesis in plants and other producers, which in turn supports the entire food web.

What is an example of an exception to sunlight as the principal energy source in most ecosystems?

• An exception to sunlight as the primary energy source in most ecosystems is found in deep-sea hydrothermal vent ecosystems, where organisms derive energy from chemosynthesis, using chemicals like hydrogen sulfide instead of sunlight. 

Food Chain

• A linear sequence of organisms where each organism serves as a food source for the next, demonstrating the transfer of energy and nutrients in an ecosystem, starting with producers and ending with decomposers.

Producers

• Organisms like plants that create their own food through photosynthesis

Consumers

• Organisms that eat other organisms for energy. 

Apex Predator

•  The animal at the very top of the food chain, with no natural predators of its own.

What do the arrows indicate in a food chain?

•  The direction of energy flow and nutrient transfer, pointing from the organism being eaten (prey) to the organism that eats it (predator). 

Image of a Food Chain

Why are food webs better at representing the trophic relationships in an ecological community than a food chain?

• They depict the complex, interconnected feeding relationships within an ecosystem, while food chains are simplistic, linear models.

Decomposer

• (Bacteria and Fungi) Break down dead organisms and organic waste, releasing nutrients back into the ecosystem for producers to use, thus completing the cycle of life and maintaining ecosystem health. 

What are some examples of decomposers?

1. Bacteria

2. Fungi

3. Earthworms

4. Millipedes

5. Certain Insects

Autotroph

• An organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide.

Carbon Fixation

• The process by which inorganic carbon (like CO2) is converted into organic compounds, such as sugars, by living organisms, primarily plants and some bacteria, during photosynthesis

Who do autotrophs “fix” carbon?

• They need to convert inorganic carbon (like CO2) into organic compounds (like sugars) that they can use as building blocks and a source of energy, a process essential for their survival and the broader ecosystem

What are the two primary uses of energy in autotrophs?

1. Building Organic Molecules: Autotrophs, like plants and some bacteria, use energy (from sunlight or chemicals) to convert inorganic substances (like carbon dioxide and water) into organic compounds, such as glucose, which they then use as food and building blocks for their bodies.

2. Powering Cellular Processes: The energy stored in these organic molecules is then used to power various cellular activities, including growth, repair, and reproduction.

Phototrophs

• Use light energy as a source of energy for synthesizing organic compounds and to power a series of oxidation reactions to release energy

Chemoautotrophs

• Synthesize carbon compounds by a series of oxidation reactions using inorganic compounds

What are some examples of photoautotrophs?

• Cyanobacteria 

• Plants

• Chlorobiaceae

What are some examples of chmoautotrophs?

• Hydrogenovibrio Crunogenus

How does oxidation reaction serve as a source of energy in iron-oxidizing bacteria?

• Iron-oxidizing bacteria, or chemolithotrophs, derive energy by oxidizing ferrous iron (Fe2+) to ferric iron (Fe3+), using the released electrons to power ATP synthesis and other cellular processes.

Heterotroph

• An organism deriving its nutritional requirements from complex organic substances.

What is the function of digestion, assimilation, and synthesis of carbon compounds in heterotrophs?

• Digestion breaks down complex food molecules

• Assimilation uses the resulting simpler molecules for growth and repair

• Carbon compound synthesis utilizes these molecules to build new cellular structures.

How do both autotrophs and heterotrophs perform cellular respiration to produce ATP?

• Both autotrophs and heterotrophs utilize cellular respiration to break down glucose and produce ATP, the cell's primary energy currency, through a series of metabolic reactions.