Please enable JavaScript.
Coggle requires JavaScript to display documents.
Population and Community Ecology - Coggle Diagram
Population and Community Ecology
Chapter 53: Population Ecology
53.1
Population
Group of individuals of a single species living in the same general area
Members rely on the same resources
Influenced by similar envrionmental factos
Interact and breed with one another
Described by their boundaries and size
Different types of boundaries
Natural
Island or a lake
Investigator
Specific county in Minnesota for a study of oak trees
Density and Dispersion
Density
Number of individuals per unit area or volume
Can be determined by counting all individuals within the boundaries of the population
Ecologists use various sampling techniques to estimate densities and total population size
Calculating
Number of oak trees in several randomly located 100 X 100m plots
Calculate the average density in the plots and then extend the estimate to the population size in the entire area
Most accurate when there are many sample plots and when the habitat is fairly homogeneous
Estimate density from an indicator of population size
Number of nest, burrows, tracks, or fecal droppings
Mark- Recapture Method
Estimate the size of wildlife populations
Can increase or decrease over time as individuals are added or removed from a population
Immigration
Influx of new individuals from other areas
Emigration
Movement of individuals out of a population and into other locations
Dispersion
Pattern of spacing among individuals within the boundaries of the population
Spacing among individuals may differ substantially creating contrasting patters of dispersion
Differences in spacing can provide insight into the biotic and abiotic factors that affect individuals in the population
Clumped
Most common pattern of dispersion
Individuals are aggregated in patches
Animal clumping can be associated with mating behavior
Aggregation of individuals into groups can increase the effectiveness of predation or defense
Uniform
Result from direct interactions between individuals in the population
Evenly spaced
Territoriality
Defense of a bounded physical space against encroachment by other individuals
Random
Position of each individual in a population is independent of other individuals
Unpredictable spacing
Absence of strong attractions or repulsion among individuals
Key physical or chemical factors are relatively constant across the study area
Demographics
Biotic and Abiotic factors that influence population density and dispersion patters
Influence other characteristics of populations like birth, death, and migration rates
Demography
Study of these key chracteristics of populations and how they change over time
Life Tables
Summarizes the survival and reproductive rates of individuals in specific age-groups within a population
Cohort
Group of individuals of the same age from birth until all individuals are dead
Survivorship Curves
Survival rate data in a life table
Plot of the proportion or numbers in a cohort still alive at each age
Type II curve
High death rates for the young but it flattens out as death rates decline for those few that survive the early period of die-off
Organisms produce very large numbers of offspring but provide little or no care
Type III curve
Mortality is high no matter the age group
Type I curve
Low death rate during early and middle life but high death rates among the older age groups
Few offspring but the offspring are taken good care off
53.2
Populations of all species have the potential to expand greatly when resources are abundant
Ecologists study population growth in ideal, unlimited environments to reveal how fast populations are capable of growing and the conditions under which rapid growth might occur
Changes in Population Size
Few individuals living in an ideal unlimited environment
Population increases in size with every birth and with the immigration of individuals from other populations
Decrease in size with every death and with the emigration of individuals out of the population
Change on population size = Births + Immigrants entering population - Deaths - Emigrants leaving population
Mathematical notation
N
Population size
t
Time
Triangle N
Change in population size
Triangle t
Time interval
generation time of the species
B
Number of births in the population during the time interval
D
Number of deaths
R
Difference between the number of births and the number of deaths that occure in the time interval
Exponential growth
Growth of a population in an ideal, unlimited environment, represented by a J-shaped curve when population size is plotted over time
dN/dt represents the rate at which the population is increasing in size at each moment in time
r
Intrinsic rate of increase
per capita rate at which an exponentially growing population increases in size at each instant in time
New individuals are added per unit of time when the population is larger than when it is small resulting in the curve becoming steeper over time
Occurs because population growth depends on N as well as r
Population with a higher intrinsic rate of increase will grow faster than one with a lower intrinsic rate of increase
J - Shaped curve
Characteristic of some populations that are introduced into a new environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding
53.3
As the population size increases each individual has access to fewer resources
Limit to the number of individuals that can occupy a habitat
Carrying capacity
The maximum population size that can be supported by the available resources
K
Maximum population size that a particular environment can sustain
Varies over space and time with the abundance of limiting resources
Limiting factors
Energy
Shelter
Refuge from predators
Nutrient avaliability
Water
Suitable nesting
If individuals cannot obtain sufficient resources to reproduce then the per captia birth rate will decline
If starvation or disease increases with density, then the per capita death rate may increase
Logistic Growth model
Per capita rate of population growth approaches zero as the population size nears the carrying capacity (K)
If carrying capacity is K, then K - N is the number of additional indiciduals the envrionment can support
Produces a sigmoid (S - shaped) growth curve when N is plotted over time
For a population's growth rate to decrease the birth rate must decrease, the death rate must increase or both
Logistic Model and Real Populations
Growth of laboratory populations of some small animals fit an S-shape curve fairly well under conditions of limited resources
Populations are grown in a constant environment lacking predators and competing species that may reduce growth of the population
Assumes that populations adjust instantaneously to growth and approach carrying capacity smoothly
If food becomes limiting for a population the reproduction will decline eventually but females may use their energy reserves to continue reproducing for a short time
May cause the population to overshoot it carrying capacity temporarily
Provides a useful starting point for thinking about how populations grow and for constructing more complex models
Important in conservation biology for predicting how tapidly a particular population might increase in numbers after it has been reduced to a small size and for estimating sustainable harvest rates for wildlife populations
53.4
Natural selection favors traits that improve an organisms chances of survival of survival and reproductive success
Life History
Traits that affect an organisms schedule of reproduction and survival
Evolutionary outcomes reflect in its development, physiology, and behavior
Diversity of Life Histories
When reproduction begins (age at maturity)
How often the organism reproduces
How many offspring are produced per reproductive episode
Fundamental idea that evolution accounts for the diversity of life is manifest in the broad range of these life history characteristics in nature
Organisms vary in how often they reproduce
Semelparity
One - shot pattern of big-bang reproduction
Salmon
Century plant
Iteroparity
Repeated reproduction
Female loggerhead turtle produces four clutches totaling approximately 300 eggs in a year
Trade-offs and life histories
Tradeoff between the number of offspring and the amount of resoutces a parent can devote to each offsrping
Happens cuz organisms do not have access to unlimited amounts of resources
The use of resources for one function can reduce the resources available for supporting another function
Plants and animals who's young have a low change of survival often producr many small offspring
Animals that have suffer high predation rates like quail, sardines, and mice tend to produce many offspring
Extra investment on the part of the parent greatly increases the offsprings chanves of survival
K - selection
Traits that are advantageous at high densities
Operate in populations living at a density near the limit imposed by their resources (carrying capacity)
Mature trees gowing in an old-growth forest
R -selection
Traits that maximize reproductive success in uncrowded environments
Intrinsic increase of r
Occurs in environments in which population densities are well below carrying capacity or individuals face little competition
Conditions found in distrurbed habitats that are being recolonized
53.6
The Global Human Population
The reduction in annual growth rate observed over the past six decades shows that the human population is now growing more slowly than expected in exponential growth
Regional Patterns of Population Change
Zero population growth = Hight birth rate - Hight death rate
Zero population growth = Low birth rate - Low death rate
Demographic transition
In a stable population, a shift from high birth and death rates to low birth and death rates.
Age Structure
The relative number of individuals of each age in a population
Age - structure diagrams not only predict a populations growth trend but also can illuminate social conditions
Infant Mortality and Life Expectancy
Infant mortality
Number of infant deaths per 1,000 live births
Life expecancy at birth
Predicated average length of life at birth vary widely in different countries
These differences reflect the quality of life faced by children at birth and influence the reproductive choices parents' male
Global Carrying Capacity
Estimates of Carrying Capacity
Use curves like that produced by the logistic equation to predict the future maximum of the human population
Generalize from existing maximum population density and multiply the number this number by the area of habitable land
Other base their estimate in a single limiting factor like food and consider variables such as the amount of farmland, average yield of crops, prevalent diet, & the number of calories needed per person per day
Limits on Human Population Size
Ecological foorprint
The aggregate land and water area required by a person, city, or nation to produce all of the resources it consumes and to absorb all of the waste it generates
Estimate by adding up all the ecologically productive land on the planet and divide by the size of the human population
Made using global hectares where a global hectare represents a hectare of land or water with a productivity equal to the average of all biologically productive areas on earth
No single carrying capacity how many people our planet can sustain depends on the quality of life each of us has and the distribution of wealth across people and nations
We can decide whether zero population growth will be attained through social changes based on human choices or through increased mortality due to resource limitations, plagues, war, and environmental degration
53.5
Population Change and Population Density
If immigration and emigration offset each other then a population grows when the birth rate exceeds the death rate and declines when the death rate exceeds the birth rate
Density Independent
Any characteristic that is not affected by population density
Variation such as temperature and precipitation can cause dramatic changes in population size
Can't consistently cause a population to decrease in size when it is large or in size when it is small
Density Dependent
Any characteristic that varies with population density
Consistently cause a population to decrease in size when it is large or increase in size when it is small
Changes in birth and death rates curb population increase through negative feedback & can eventually stabilize a population near its carrying capacity
Limitations
intraspecific competitions for limited food or space
Increased predation
Disease
Intrinsic physiological factors
Population is said to be regulated when one or more density -dependent factors cause its size to decrease when large or increase when small
All populations exhibit some size fluctuations
Changing environmental conditions periodically disrupt them
Many populations undergo regular boom and bust cycles that are influenced by complex interactions between biotic and abiotic factors
Metapopulation
group of populations linked by immigration and emigration
Chapter 54: Community Ecology
54.1
interspecific interactions
A relationship between individuals of two or more species in a community
Competition
-/-
Individuals of different species each use a resource that limits the survival and reproduction of both individuals
Competition for resources can also occur between members of the same species
Competitive exclusion
concept that when populations of two similar species compete for the same limited resources, one population will use the resources more efficiently and have a reproductive advantage that will eventually lead to the elimination of the other population
Predation
+/-
positive effect on the survival and reproduction of members of the predator population
negative effect on members of the prey population
Herbivory
+/-
organism eats parts of a plant thereby harming it but usually not killing it
Parasitism
+/-
Derives its nourishment from another organism its host which is harmed in the process
endoparasites
Parasite that lives within a host
ectoparasites
parasite that feeds on the external surface of a host
Mutualism
+/+
Survival and reproduction of individuals of each species is increased in the presence of the other
Zero indicates that the members of a species are not affected by the interaction
Commensalism
+/0
Interaction that benefits the individuals of one of the interacting species but neither harms nor helps the individuals of the other species
Exploitation
+/-
One species benefits by feeding on individuals of the other species
Includes predation, herbivory, and parasitism
Ecological Niches and Natural Selection
ecological niche
The sum of a species’ use of the biotic and abiotic resources in its environment
Two species cannot coexist permanently in a community if their niches are identical
species can coexist in a community if one or more significant differences in their niches arise through time
resource partitioning
division of environmental resources by coexisting species such that the niche of each species differs by one or more significant factors from the niches of all coexisting species
Character Displacement
Closely related species whose populations are sometimes allopatric (geographically separated) and sometimes sympatric (geographically overlapping) provide additional evidence of how competition affects communities
In some cases, the allopatric populations of such species are morphologically similar and use similar resources
tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
Defensive adaptations in animals
Mechanical or chemical defenses protect species
Porcupines
Skunks
Aposematic coloration
warning colors
Animals with effective chemical defenses often exhibit bright coloring
Cryptic coloration
Camouflage
Batesian mimicry
a harmless species resembles an unpalatable or harmful species to which it is not closely related
Müllerian mimicry
Reciprocal mimicry by two unpalatable species
54.2
Species diversity
The number and relative abundance of species in a biological community
Relative abundance
proportional abundance of different species in a community
species richness
number of species in a biological community
Comparing the density of communities
Calculate indexes of diversity based on species richness and relative abundance
Shannon diversity index (H)
A, B, C are the species in the community
p is the relative abundance of each species
In is the natural logarithm
Higher value of H indicates a more diverse community
Diversity and Community Stability
Ecologists manipulate diversity in experimental communities in nature and in the laboratory
Examine the potential benefits of diversity including increased productivity and stability of biological communities
Higher diversity communities generally are more productive and are better able to withstand and recover from environmental stresses like droughts
Higher- diversity communities are often more resistant to introduced species
Trophic Structure
The different feeding relationships in an ecosystem, which determine the route of energy flow and the pattern of chemical cycling
trophic level
The position an organism occupies in a food chain
Food Webs
Group of food chains are linked together to create it
Ecologists diagram the trophic relationships of a community using arrows that link species according to who eats whom
Complicated food webs solutions
Species with similar trophic relationships in a given community can be grouped into broad functional groups
Isolate a portion of the web that interacts very little with the rest of the community
Limits on Food Chain Length
only a few links long
energetic hypothesis
concept that the length of a food chain is limited by the inefficiency of energy transfer along the chain
Species with a Large Impact
Foundation species
A species that has strong effects on its community as a result of its large size, high abundance, or pivotal role in community dynamics
keystone species
species that is not necessarily abundant in a community yet exerts strong control on community structure by the nature of its ecological role or niche
ecosystem engineers
An organism that influences community structure by causing physical changes in the environment
Bottom-up control
situation in which the abundance of organisms at each trophic level is limited by nutrient supply or the availability of food at lower trophic levels
the supply of nutrients controls plant numbers, which control herbivore numbers, which in turn control predator numbers
Top-down control
the abundance of organisms at each trophic level is controlled by the abundance of consumers at higher trophic levels
predators limit herbivores, and herbivores limit plants
54.3
nonequilibrium model
model that maintains that communities change constantly after being buffeted by disturbances
Ecolofical Succession
Transition in the species composition of a community following a disturbance; establishment of a community in an area virtually barren of life
primary succession
type of ecological succession that occurs in an area where there were originally no organisms present and where soil has not yet formed
secondary succession
type of succession that occurs where an existing community has been cleared by some disturbance that leaves the soil or substrate intact
Characterizing Disturbance
Intermediate disturbance levels rarely create conditions so severe that they exceed the environmental tolerance or recovery rates of potential community members
Intermediate disturbance hypothesis
concept that moderate levels of disturbance can foster greater species diversity than low or high levels of disturbance
Fire
Stream pons
Storms
Low disturbance levels can result from either a low frequency or low intensity of disturbance
High level of disturbance is generally the result of frequent and intense disturbance
High levels of disturbance reduce diversity by creating environmental stresses that exceed the tolerance of many species
Low levels of disturbance can reduce species diversity by allowing competitively dominant species to exclude less competitive ones
53.4
Large scale biogeographic factors also contribute to the tremendous range of diversity observed in biolofical communities
Latitudinal Gradients
1850 Charles Darwin and Alfred Wallace pointed out that plant and animal life was generally more abundant and diverse in the tropics than in othet parts of the globe
Key factors that can affect latitudinal gradients of species richness
Evolutionary history
Climate
Evapotranspiration
total evaporation of water from an ecosystem, including water transpired by plants and evaporated from a landscape, usually measured in millimeters and estimated for a year
Area Effects
1807 naturalist and explorer Alexander von Humboldt described one of the first patterns of species richness to be recognized the species- area curve
Species-area curve
The biodiversity pattern that shows that the larger the geographic area of a community is, the more species it has
54.5
Pathogens
Disease causing microorganisms, viruses, ciroids, or prions
Can be particularly virulent in a new habitat because new host populations have not had a chance to become resistant to the pathogen through natural selection
Effects on Community Structure
Effect on coral reef communities
Disease kills corals by causing their tissue to slough off in a band from the base to the tip of the branches
staghorn coral has virtually disappeared from the Caribbean
elkhorn coral have also been decimated
this coral used to be key habitat for lobsters, snappers, and other fish
When coral dies, they become overgrown algae and surgeonfish and other herbivores that feed on it come to dominate the fish community
Community Ecology and Zoonotic Diseases
zoonotic pathogens
A disease-causing agent that is transmitted to humans from other animals
Community ecology provides the framework for identifying key species interactions associated with such pathogens and for helping us track and control their spread
vector
An organism that transmits pathogens from one host to another
Parasites
Ticks
Lice
Mosquitoes