APES U3

Generalist species

Species that can live under a wide range of biotic and abiotic conditions, have a varied diet, broad niche, and high adaptability, making them less prone to extinction and more likely to be invasive.

Specialist species

Species that live under a very narrow range of conditions, feed on one or a very small group of species, require specific resources, have narrow niches, and are more vulnerable to extinction when conditions change.

Exponential growth

When a population increases by a fixed percentage each year, displayed graphically as a J-curve.

Logistic growth

Describes how a population's initial exponential increase is slowed and eventually stabilized by environmental limiting factors, shown as an S-curve.

Carrying capacity ($K$)

The maximum number of individuals of a given species that a particular environment can sustainably support.

Overshoot

When a population temporarily exceeds its environment's carrying capacity, leading to resource depletion.

Dieback

A sharp population crash that occurs following an overshoot event due to limited resources, famine, or disease.

Limiting factors

Environmental characteristics (such as food, water, space, and predators) that constrain and regulate population growth.

Density-dependent factors

Limiting factors whose influence changes with population density, such as competition, predation, and disease.

Density-independent factors

Limiting factors whose influence is unaffected by population density, such as extreme weather events (droughts, floods).

Biotic potential

The maximum reproductive growth rate of a population under ideal, optimal environmental conditions.

Factors influencing biotic potential

Gestation time (time for a fetus to develop), generation time (age at which individuals have their own offspring), and fecundity (number of offspring born to an individual).

r-Selected species

Organisms that prioritize high growth rates by producing many small offspring, providing little to no parental care, maturing early, and having short lifespans (e.g., dandelions, frogs, most invasive species).

K-Selected species

Organisms that live in stable environments, have long lifespans, produce few offspring, and invest significant energy into heavy parental care and late maturation (e.g., humans, elephants, whales).

Birth and death rates

The primary direct demographic factors that determine whether a population's size increases or decreases.

Immigration and emigration

The arrival of individuals from outside an area (immigration) versus the departure of individuals from an area (emigration).

Survivorship curves

Graphs showing how the likelihood or probability of death and survival varies across different ages in a population from birth to death.

Type I survivorship curve

Curves characterized by high survival rates through youth and adulthood, with higher mortality concentrated at older ages (common in K-selected species like humans).

Type II survivorship curve

Curves showing a constant, steady mortality rate regardless of age (common in birds and some reptiles).

Type III survivorship curve

Curves reflecting very high mortality rates early in life, with few individuals surviving to older ages (common in r-selected species like trees and fish).

Age structure diagrams

Visual population pyramids showing the distribution of various age groups (pre-reproductive, reproductive, post-reproductive) broken down by gender, used to predict future population growth.

Total Fertility Rate (TFR)

An estimate of the average number of children that each woman in a population will have throughout her reproductive lifespan.

Replacement level fertility

The TFR level required for a population to exactly replace itself from one generation to the next, which is roughly 2.1 in developed countries.

Factors affecting human TFR

Nutrition/agriculture access, health/sanitation (clean water and lower infant mortality), female educational opportunities, family planning/birth control access, and government policies (e.g., China's One-Child Policy).

Infant mortality rate

The annual number of deaths of children under one year of age per 1,000 live births.

Life expectancy

The average number of years that a human newborn can be expected to live under current mortality conditions.

Thomas Malthus

An economist who hypothesized in 1798 that human population grows exponentially while food supply grows linearly, predicting that population would eventually outstrip resources.

Crude Birth Rate (CBR) and Crude Death Rate (CDR)

The number of live births and deaths respectively per 1,000 individuals in a population per year.

Rate of Natural Increase ($r$)

The percentage growth rate of a population, calculated as $(CBR - CDR) / 10$.

Rule of 70

A formula used to calculate a population's doubling time by dividing 70 by the percentage growth rate ($\text{Doubling Time} = 70 / r$).

Demographic transition

The historical shift of a country from high birth and death rates to low birth and death rates as it undergoes economic and social industrialization.

Stage 1 (Preindustrial)

Characterized by high infant mortality, high death rates, and high birth rates due to lack of healthcare, clean water, and education, resulting in little to no population growth.

Stage 2 (Industrializing/Developing)

Characterized by rapidly declining death rates and infant mortality due to improved food production and sanitation, while birth rates remain high, leading to rapid population expansion.

Stage 3 (Developed/Industrialized)

Characterized by falling birth rates and a declining TFR as urbanization, increased educational opportunities for women, and family planning take effect.

Stage 4 (Post-Industrialized)

Characterized by low birth and low death rates, resulting in a stable or low-stationary total population where TFR may drop below replacement levels.