# Set 5 - Part 2 - Population Ecology - Khan Academy

celine's version from 2018-02-21 23:33

## Section 1

A ____________ consists of all the organisms of a given species that live in a particular area.population
The statistical study of populations and how they change over time is calleddemography
Two important measures of a population are ____________, the number of individuals, and ____________, the number of individuals per unit area or volume.population size, population density
Ecologists estimate the size and density of populations using ___________ and the ___________.quadrats and the mark-recapture method
The organisms in a population may be distributed in a ____________, ____________, or ____________ pattern. ____________ means that the population is evenly spaced, ____________ indicates random spacing, and____________ means that the population is distributed in clusters.uniform, random, clumped, uniform, random, clumped
The statistical study of any population, human or otherwise, is known asdemography
Why is demography important?Populations can change in their numbers and structure for various reasons. These changes can affect how the population interacts with its physical environment and with other species. By tracking populations over time, ecologists can see how these populations have changed and may be able to predict how they're likely to change in the future.
2 baseline measures used to study the demographics of a populationpopulation size & population density
The number of individuals in the populationpopulation size
The number of individuals per area or volume of habitatpopulation density
2 most important methods used to sample populations to determine their size and densityquadrats and the mark-recapture method
A square or rectangular plot of land used to mark off at random a physical area to isolate a sample and determine the percentage of vegetation and animals occurring within the marked area.Quadrat
For immobile organisms such as plants or for very small and slow-moving organisms ____________may be used to determine population size and density.Quadrats
For organisms that move around, such as mammals, birds, or fish, a technique called the ____________ is often used to determine population size. mark-recapture method
In addition to knowing the number and density of individuals in an area, ecologists also check their distribution. ____________ refers to how the individuals in a population are distributed in space at a given time.dispersion patterns or distribution patterns

## Section 2

To predict if a population will grow or shrink, ecologists need to know birth and death rates for organisms at different ages as well as the current age and sex makeup of the population. ____________ summarize birth and death rates for organisms at different stages of their lives.Life tables
____________ are graphs that show what fraction of a population survives from one age to the next.Survivorship curves
____________ is a "snapshot" of a population in time showing how its members are distributed among age and sex categories.An age-sex pyramid
Survivorship curves can be divided into three types based on their shapes. They are Type I survivorship curve, Type II, Type III
Type I survivorship curveHumans and most primates have a Type I survivorship curve. They tend not to die when they are young or middle-aged but, instead, die when they become elderly. They usually have small numbers of offspring and provide lots of parental care to make sure those offspring survive.
Type II survivorship curveMany bird species have a Type II survivorship curve. They die more or less equally at each age interval and may also have relatively few offspring and provide significant parental care.
Type III survivorship curveTrees, marine invertebrates, and most fish have a Type III survivorship curve. Here, very few organisms survive their younger years but, the lucky ones that make it through youth are likely to have pretty long lives after that. Usually have lots of offspring at once—such as a tree releasing thousands of seeds—but don't provide much care for the offspring.
The pattern of survival and reproduction events typical for a member of the species (essentially, its lifecycle).life history
Life history patterns evolve by ____________, and they represent an "optimization" of tradeoffs between growth, survival, and reproduction.natural selection
Examples of tradeoffs in life history strategies1. Parental care and fecundity 2. Timing of first reproduction 3. Semelparity & iteroparity
1. Parental care and fecunditytradeoff between number of offspring produced and the amount of energy (both physical resources and parental care) put into each offspring.
An organism's reproductive capacity (the number of offspring it's capable of producing). fecundity
2. Timing of first reproductionTiming of first reproduction is another tradeoff. Early reproduction lowers the chance of dying without offspring, but later reproduction may allow organisms to have more or healthier offspring or to provide better care.
3. Semelparity & iteroparityMembers of some species reproduce only once (semelparity), while members of other species can reproduce multiple times (iteroparity).
In ____________, a member of a species reproduces only once during its lifetime and then dies.semelparity; Examples of species that display semelparity are bamboo, which flowers once and then dies, and the Chinook salmon, which uses most of its energy reserves to migrate from the ocean to its freshwater nesting area, where it reproduces and then dies.
In ____________, individuals of a species reproduce repeatedly during their lives. iteroparity

## Section 3

A population of minnows in a pond is growing under natural conditions with limited resources. As the minnow population increases in size, how will its rate of growth affect its population density?As the populations grows, population density increases. As a result, the rate of population growth eventually slows.
Fecundity refers to the number of offspring an organism is capable of producing. What do species with low fecundity have in common?They have high parental care.
Explain the difference between semelparous and and iteroparous species?Semelparous species reproduce once in their lifetime, while iteroparous species reproduce multiple times.
In ____________, a population's per capita (per individual) growth rate stays the same regardless of population size, making the population grow faster and faster as it gets larger.exponential growth
In nature, populations may grow exponentially for some period, but they will ultimately be limited by ____________ availability.resource
In ____________, a population's per capita growth rate gets smaller and smaller as population size approaches a maximum imposed by limited resources in the environment, known as the ____________ (K).logistic growth, carrying capacity
Exponential growth produces a ____________, while logistic growth produces an ____________.J-shaped curve, S-shaped curve
An example of exponential growthBacteria grown in the lab
An example of Logistic growthYeast, a microscopic fungus used to make bread and alcoholic beverages, can produce a classic S-shaped curve when grown in a test tube.
In nature, population size and growth are limited by many factors. Some are ____________, while others are ____________.density-dependent, density-independent
____________ limiting factors cause a population's per capita growth rate to change—typically, to drop—with increasing population density. One example is competition for limited food among members of a population.Density-dependent
____________ factors affect per capita growth rate independent of population density. Examples include natural disasters like forest fires.Density-independent
Limiting factors of different kinds can interact in complex ways to produce various patterns of population growth. Some populations show ____________, in which population size changes predictably in a cycle. For instance, predation, parasite infection, and fluctuation in food availability have all been shown to drive oscillations. These density-dependent factors don't always create oscillations, however. Instead, they only do so under the right conditions, when populations interact in specific ways.cyclical oscillations
____________ are repeating rises and drops in the size of the population over time. cyclical oscillations