Unit 3 Review Book Flashcards
(29 cards)
TErms Used to Decribe Populations
A population - a group of organisms of the same species that inhabits a define geographic area at the same time
Individuals in a population generally breed with one another realy on the same resources to live, and are influenced by the same factors in their environment
Two important characteristics of populations are the density of the population and how the population is dispersed
Population density - refers to the number of individuals of a population that inhabit a certain unit of land or water area ex. Number of squirrels that inhabit a particular forest
Population dispersion - refers to how individuals of a population are spaced within region
types of population dispersion - uniform, random, clumped
Uniform dispersion - members of the population are uniformly spaced throughout their geographic region, seen in forests, in which trees are uniformly distributed so that each receives adequate light and water, often the result of competition for resources in an ecosystem
Random - position of each individual is not determined or influenced by positions of other members of population, ex. Species of plants interspersed infields or forests, location of their growth is random and relative to other species, not their population
Clumped - individuals “flock together,” make sense for many species, many species of plants tend to grow together in a location or habitat that is near their parents and suits their requirements for life, fish swim in schools to avoid predation, birds and other animals migrate in groups
Population Growth
Biotic potential - amount that the population would grow if there were unlimited resource in its environment, not practical
Carrying capacity - is defined as the maximum population size for a species that can sustainably be supported by the available resources in that environment
A given geographic region will have different carrying capacities for populations of different species, because different species have different requirements for life
These differences in population size may be riven not just by the different sizes of individual organisms of each species, but by each species’ resource requirements and the particular array of resources available in the area
Exponential population growth
Growth of bateria with food, growth would increase exponentially, be a J-Curve
This exponential population growth rate is seen where resources are unlimited, but i nature, such ideal conditions are rare and fleeting
In reality, resource availability and the total resource base are limited and finite on any timescale
Logistic population growth
In a more realistic model for population growth, after the initial burst in population, the growth rate generally drops, and the curve ultimately resembles a flattened S
This type of growth, which is a much etter model for what exists in natural settings, is called logistic population growth
The logistic growth model basically says that when populations are well below the size dictated by the carrying capacity of the region they live in, they will grow exponentially but as they approach the carry apacity, the resource base of the population shrinks relative to the population itself
This lead to increased potential for unequal distribution of resources, which will ultimately result in increased mortality, decreased fecundity, or both
The result is that population growth declines to, or below, carrying capacity, and the size of the population will eventually become stable
If the slowdown of population growth is the result of increased mortality rather than decreased fecundity, the reality tends to be a little messier than the world slowdown implies: it will probably involve overshoot, which occurs when a population exceeds its carrying apaacity
Population overshoot
If the slowdown of population growth is the result of increased mortality rather than decreased fecundity, the reality tends to be a little messier than the world slowdown implies: it will probably involve overshoot, which occurs when a population exceeds its carrying apaacity
There are environmental imapcts of population overshoot, including resource depletion
If resource depletion is severe enough, teh carrying apacity of the environment may be lowered
The severity of these effects varies, but resource depletion generally leads to dieback of the population which can be severe to catastrophic, because the lack of available resources leads to famine, disease, and/or conflict
Once the dieback occurs, the population once again falls below carrying capacity; if the events were not too catastrophic, the environment can recover and the reduction in carrying capacity may not be permanent
Population doubling time
We can use a model called the Rule of 70
Says that the time it takes in years for a population to double an be approximated by dividing 70 by the current growth rate of the population
Ex. growth rate = 5 percent, 70 divided by 5 = 14 years for population to double
r-selected organisms
Have populations below the carrying capacity of their environment, means that population growth is constrained only by the species’ own biological limits
Competition for resources in r-selected species’ habitats is usually relative low
These organisms tend to be small and have short life spans; they mature and reproduce early in life and have many offspring at once - they may have so many that they reproduce only once in a life time
Thuse they have a high capacity for reproductive groth
Ex. bacteria, algae, and protozoa
Little or no care is given to offspring, but due to sheer numbers of offspring, enough of offspring will survive to enable the population to continue
K-selected organisms
Have populatiosn whose growth is limited by the carrying capacity of the environment; live in stable environments where competition for resources irs relatively high
Tend to be large and have longer life spans
Mature and reproduce later in life after years of parental care, produce fewer offspring per reproduction event (but tend to reproduce more than once in their lifetimes0, and devote significant time and energy to the nurture of offspring
It is important to rpeserve as many members of the offspring as possible because they rpdouce so few, parents have a tremendous investment in each individual offspring
Ex. humans, lions, and cows
classification in r or K selected
Invasive species tend to be r-selected, while the species most adversely affected by invasives tend to be K-selected
for the same reason, generalists tend to be r-selected while specialists are K-selected
Many species lie on the continuum between these two strategies, and some can change strategies in different conditions or at different times, but the groups are useful for broad comaprisons
Survivorship curves
Represent the number of individuals in a population born at a given time (called a cohort) that remain alive as time goes on
Different species have different survivorship curves depending on their life cycles and life strategies, including r and K-selection
Survivorship curves differ for K-selected and r-selected species: K-selected species typically follow a Type I or Type II curve, while r-selected species tend to follow a type III curve
Type I (K-selected)
the convex shape of this curve indicates that most individuals in teh population survive into adulthood with a sharp increase in mortality as the population approaches the species’ maximum age
Type II
Mortality and survival rates are fairly constant throughout life, many bird species, mice, and some species of lizards exhibit this straight-line patterns
Type III (r-selected)
the convex shape indicates that most offspring die young, but if they live to a certain age, they will live a longer life
species with this curve produce high numbers of offspring that encounter bottlenecks to survival that wipe out most young, and parents provide little or no nurture to their young,
ex. Plants that produce millions of seed throughout their lifetimes and most marine invertebrates
Clams, for example, produce millions of eggs, but the larvae are highly vulnerable to dying off from ocean currents and predators, the individuals that live long enough to develop their shell, however, will live to advances age
Most actual populations exhibit some combination of these patterns
(survivorship curves)
Ex. at some point in human history, infant mortality has been unusually high, resulting a sharp dip in the survivorship curve before it flattens out to typical shape
Ex. crustaceans like crabs and lobsters are most vulnerable while molting (replacing their shell), since these species molt regularly throughout their lives, their survivorship curves show a stair-step pattern
Boom-and-Bust Cycle
Very common among r-strategists
In this type of cycle, there is a rapid increase in the population adn then an equally rapid drop-off
These rapid changes may be linked to predictable cycles in the environment (temperature or nutrient availability, for example)
These cycles may reflect regular changes in rainfall, temperature, or nutrient availability over the course of the year
Or they may reflect longer and leeds regular cycles
When the conditions are good for growth, teh population increases rapidly
When the conditions for that population worsen, its numbers rapidly decline
Strategy is “get it while the getting’s good”
Predator-Prey Cycle
Rabbits and coyotes, in a year of relatively high rainfall, rabbits have plenty of food, which enables them to reproduce very successfully, inturn because the coyote is a predator of the rabbit, coyotes would also have plenty of food, and their populations would laso rise rapidly
However, if the rainfall is velow average a few years later, then there would be less grass, the population of rabbits would decline, and the coyote population would decline in turn
ADD GRAPH
Important - coyote doens’t change at exactly the same time as the rabbit population, but after, because rabbit population has to have time to build up to fairly high levels before coyotes can find enough to eat
Plays a role in understanding why many endangered species are large carnivores
Large predator opopulations can suffer directly if humans alter their natural habitas, but they can also suffer indirectly if humans kill of their prety
If the prey population falls so low that the repdator cannot find food, then the predator population will decline,s sometimes to the point of extinction
Density dependent factors
influencing population growth
Population-limiting factors that are purely the result of the size of the population itself
Ex. in many populations of species in nature, birth and death rates are influenced by the density of the population
Other density dependent factors that influence population size are increased predation (which occurs because there are more members of the population to attract predators); competition for food or living space; disease (which can spread more rapidly in overcrowded populations); and the buildup of toxic materials
Density independent factors influencing population growth
Population-limiting factors which operate independently of the population size
Will change the population’s size regardless of whether the population s large or small
These include fire, storms, earthquakes, and other catastrophe events
F
Rate of population change
[(birth rate +immigration rate) - (death rate + emigration rate)] / 10
All rates in the formula are raw numbers per 1000 people per year
Ex. birth rate (crude birth rate) is equal to the number of live births per 1000 members of the population
Death rate (or crude death rate) is equal to the number of birth per 1000 members of the population in a year
A Simple version of the formula, called the Actual Growth Rate, excluding immigration and immigration: (birth rate - death rate)/10
people in the US
about 340 million
what do population statistics suggest
Statistics on median age are one indication of quality of life, while the information on population density suggests that not all densely populated countries are poor and not all sparsely populated countries are prosperous
How Do Human Populations Change?
Populations can also change in number as a result of migration into nd out of the population
Emigration - movement of people of a population
Immigration - which is the movement of people into a population
In annual growth rate formula, immigration and emigration would also need to be expressed as rates per thousand in the population
In general, emigration and immigration are only small factors in the changes in size of human population; however, the US, unlike many other highly developed countries, has the third-largest population due to immigration
Most significant additions to human populations are due to births, total fertility rate
Most significant additions to human populations are due to births, total fertility rate
The term total fertility rate is used to describe the number of children a woman will bear during her lifetime, and this information is based on an analysis of data from preceding years for the population in question
Total fertility rates are predictions that provide a rough estimate, but they can’t be depended on because they assume that the conditions of the past will be the conditions of the future
