unit 1- population dynamics

global resource use

is the total amount of natural resources extracted and consumed worldwide within a given period of time (usually one year) to support human needs and economic activity.

resource use across the globe

Resource use across the globe is how countries and populations extract and consume natural resources worldwide over time to support human needs and development.

needy ppl often struggle to survive and b/c there is a diff in resource distribution among ppl- impact pop growth

types of resources

fresh water- only 0.003% can drink

wood- important of co2 and o2

food- urbansettelments lead to deforestation and an increase demand for food

non-renewable energy- sources that will run out and will not replenish in a lifetime ex. fossil fuels

renewable energy- don’t ever run out ex. wind

metal and minerals- natural inorganic substances found in the earths crust

land- important cuz all agriculture, animals, and forestry production depend on land productivity

human carrying capacity

the largest population that can live on Earth (or in an area) sustainably, given the available resources

robert malthus

theory of population (1798) suggested that human population grows faster than the food supply. He believed population increases exponentially (1, 2, 4, 8...) while food production grows only arithmetically (1, 2, 3, 4...). Eventually, this imbalance would lead to famine, disease, and war, which Malthus called “natural checks” that reduce population size back to sustainable levels.

voluntary- birth control

involuntary- war, famin, disease

ecological footprint

a measure of how much land, water, and resources a person or population needs to produce what they consume and absorb the waste they generate. It is measured in global hectares (gha) — units that represent the biologically productive area of land and sea needed to support that level of consumption.

factors affecting human pop growth

• in developed countries birth rates have declined and the pop would shrink if it wasn’t for immigrants

• pops grow when the birth rate is higher than the mortality rate

• pops shrink when mortality rate is higher than the birth rate

• pops stay stable when the birth rate= mortality rate

demographic transition

the process by which a country’s birth and death rates change over time as it develops, moving from high to low rates.

industrial revolution

The Industrial Revolution was the shift to machine-based industry in the 1700s, which caused rapid population growth due to lower death rates, better food, and improved healthcare.

pop dispersion

describe how the individuals are dispersed over the area

pop density

Population density is the number of people per unit area of land, often shown as people per square kilometer. (how many individuals there are in a given area)

pop density (D)=total number of individuals(N)/space occupied by individuals (S)

ecological density

number of individuals in a pop per unit of suitable space rather than total area

ecological density(De)= total number of individuals (N)/ amount of suitable habitat available (Se)

clumped

Clumped dispersion is a pattern where organisms are grouped in patches, often around resources like food, water, or shelter.

uniform

Uniform dispersion is a pattern where organisms are evenly spaced, often due to competition for resources or territorial behavior.

random

Random dispersion is a pattern where organisms are distributed irregularly, with no clear reason for their placement.

quadratic

Quadrat population sampling is a technique where a square frame (quadrat) is used to count organisms in a small area, and the data are used to estimate the total population in a larger area.

limitations if organism has heavily clumpoed dispersion 

average count per quadrant= total species individual per quadrant/ number of quadrant 

mark and recapturing 

Mark and recapture is a population sampling method where animals are captured, marked, released, and then recaptured later. The number of marked animals found in the second sample is used to estimate the total population size.

total pop number(N)= total number marked*size of second sample(n)/ number of recaptures (m)

Pop growth and survivorship curves

Population growth shows how a population changes over time:

• Exponential growth (J-shaped curve): population grows rapidly when resources are unlimited.

• Logistic growth (S-shaped curve): growth slows as resources run out and reaches a carrying capacity.

Survivorship curves show how survival rates change with age:

• Type I: most survive to old age (e.g., humans).

• Type II: equal chance of dying at any age (e.g., birds).

• Type III: many die young, few survive to adulthood (e.g., fish).

survivorship and fecundity

Survivorship is the proportion of individuals that survive to different ages in a population. It shows how long members of a species typically live and is represented by survivorship curves (Type I, II, and III).

Fecundity is the average number of offspring produced by an individual during its lifetime. It measures an organism’s reproductive rate — species with high fecundity produce many offspring (like fish), while species with low fecundity produce few but invest more care (like humans).

In short:

• Survivorship = how long individuals live.

• Fecundity = how many offspring they produce.

4 factors of pop change

birth (b)

death (d)

Immigration (i)

emigration (e)

open pop

can be changed by immigration and emigration no physical barrier preventing individuals to leave or come 

closed pop

one that changes in size only through births and deaths, with no movement of individuals in or out.

net pop change

combined pop size after birth, death, immigration, emigration

net pop change=(b+i)-(d+e)

% change in pop: Percent Change=new Population- old Population/Old Population​×100

internal and external factors

internal- reproductive ability

external- weather, food, disease, predation

geometric growth model

The geometric growth model shows population growth in fixed time steps, where the population multiplies by a constant rate each period. It’s typical for species with seasonal reproduction.

Nt​=N0​(1+r)t

where:

• NtN_tNt​ = population size at time t

• N0N_0N0​ = initial population size

• rrr = growth rate (per time period)

• ttt = number of time intervals

j-shaped curve

exponential growth model

The exponential growth model shows continuous population increase where the growth rate is proportional to the current population size.- J-shaped curve

dN/dt=rN

r- growth rate/ individual

biotic potential

max pop growth rate that could occur under ideal conditions for an organism (r reaches its max)

logistic growth model

Logistic growth has three phases: a lag phase (slow start), an exponential phase (rapid increase), and a stationary phase (population stabilizes at carrying capacity (K)).

dN/dt=rN*(k-N)/K

density-dependent

Density-dependent factors are limiting factors whose effects increase as population density rises, such as competition, disease, predation, and limited food or space.

• Competition for food or mates

• Predation (more prey → more predators)

• Disease and parasites spread more easily in dense populations

• Limited resources like water, shelter, or nesting sites

density- independent

Density-independent factors are limiting factors that impact populations no matter their size, such as natural disasters, weather, climate changes, or human activities.

boom and bust

A boom-and-bust cycle is when a population grows quickly during favorable conditions (boom) and then sharply declines when resources run out or conditions worsen (bust).

pop cycle

A population cycle is a repeating pattern of population increase and decrease, often caused by interactions between species (like predators and prey) or changes in resource availability.

levels of organization in ecological systems

• Organism – A single living individual (e.g., one deer).

• Population – A group of individuals of the same species living in the same area (e.g., a herd of deer).

• Community – All the different populations living and interacting in one area (e.g., deer, trees, wolves, birds).

• Ecosystem – The community plus the nonliving (abiotic) environment like water, soil, and climate.

Hierarchy summary: individuals-pop- communities- ecosystems

habitat and Niche

Habitat- where species carry out its daily life “adress“

Niche- way of life (what it eats, activity, reproduction…)

interactions between organisims

1. interaction between 2 organisms (or species)

2. community-level interactions

competition

Competition is the interaction between organisms or species that reduces the availability of resources for one or more of them.

1. Intraspecific competition – between members of the same species (e.g., trees competing for sunlight).

2. Interspecific competition – between different species (e.g., lions and hyenas competing for prey).

Interference competition

occurs when individuals actively prevent others from using resources, such as fighting, chasing, or defending territory.

Exploitative competition

occurs when individuals compete by using up resources, rather than through direct interaction.

Interspecific competition

is when different species compete for the same resources, which can limit the growth, survival, or reproduction of one or both species.

competitive exclusion

Gause’s principle that result of competitive exclusion in nature is that very rare 2 species similar niche requirements to be in competition for very long. one will eventually out-compete the other resulting in the disappearance of the loser. 

how can species coexist?

similar species can coexist by dividing resources.

resource partitioning

when species specialize in diff subsets resources(reduce direct competition and allows multiple species to survive in the same habitat)

Predation

Predation is a relationship in which a predator feeds on its prey, helping control prey populations and maintain ecosystem balance.

morphology defenses

structural features that reduce risk of predation makes it harder for prey to be caught eaten or handled. ex. thorns, stinging hairs tec…

chemical defenses

both animals and plants use this. plants need chemicals cuz they cant escape. chemicals effects: toxic, metabolic interference. ex. skunk spray

protective colouration

uses color to defend in 2 main ways. 

1. cryptic colouration (camouflage)- helps prey blend in with surroundings

2. aposematic colouration(warning colours)- bright colours signal danger to predators that it is toxic (yellow, blue, red)

symbiosis

close relationship between 2 species where at least one benefits

mutualism

both species benefit (bacteria in human gut)

commensalism

one species benefits while the other is not affected

parasitism

one species benefits while the other (the host) is harmed. types of parasitism:

1. microparasites(microscopic)- plasmodium (protozoan) causes malaria

2. macroparasites (visible to naked eye)- endoparasites live inside a host (tapeworms) ectoparasites live on the outside (lice)

3. social parasitism- take advantage of the behaviour of another species (cuckoo birds get rid of other birds eggs in nest and replace them with their own so the other bird raises their eggs)

trophic levels

feeding hierarchy (who eats who)

food webs

interconnected food chains show ripple effects across species

food chains

linear sequence of feeding (energy transfer)