Population Ecology the study of populations in relation to environment (including environmental influences on density and distribution, age structure, and population size) A population is a group of individuals of a single species living in the same general area

Density and Dispersion Density is the number of individuals per unit area or volume Dispersion is the pattern of spacing among individuals within the boundaries of the population Most dispersion patterns are “clumped” around available resources) A uniform dispersion is one in which individuals are evenly distributed It may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals In a random dispersion, the position of each individual is independent of other individuals It occurs in the absence of strong attractions or repulsions

Biotic Factors Affecting Dispersion Biotic factors that affect the distribution of organisms may include Predation Parasitism Herbivory For example, sea urchins can limit the distribution of seaweeds Competition Behavior (Migration, mating) Abiotic Factors Affecting Dispersion Abiotic factors affecting distribution of organisms include Temperature Water Sunlight (Light intensity and wavelength affect photosynthesis) Salinity Wind Rocks and soil (Physical structure, pH,Mineral composition)

Immigration is the influx of new individuals from other areas Density is the result of an interplay between processes that add individuals to a population and those that remove individuals  LIKE BIRTH & DEATH RATES Immigration is the influx of new individuals from other areas Emigration is the movement of individuals out of a population Births Deaths Immigration Emigration Births and immigration add individuals to a population. Deaths and emigration remove individuals from a population. © 2011 Pearson Education, Inc.

There are 2 evolutionary “strategies” that help explain population growth among species: - The Exponential model (for r-selected species) - The Logistic model (for K-selected species)

The exponential model describes population growth in an idealized, unlimited environment Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth

The J-shaped curve of exponential growth characterizes: Species inhabiting areas that are plentiful in resources (food, space) Ex. Bacterial growth - Rebounding populations For example, the elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned

Limiting Factors include: In the real world…resources are not unlimited! The logistic model describes how a population grows more slowly as it nears its carrying capacity Exponential growth cannot be sustained for long in any population A more realistic population model limits growth by incorporating carrying capacity Carrying capacity (K) is the maximum population size the environment can support Carrying capacity varies with the abundance of limiting resources Limiting Factors include: Food and water availability, shelter or nesting sites, predators, pathogens/parasites (disease)

The Logistic Growth Model In the logistic population growth model, the rate of increase declines as carrying capacity is reached The logistic model of population growth produces a sigmoid (S-shaped) curve.

Parts of a Logistic Curve 3 4 1 2 1 – Lag/Establishment Period  slow growth due to small #’s in the population 2 – Log Phase/ Exponential Phase  rapid growth (doubles with each generation) 3 – Deceleration/Stationary Phase slow/no growth (reaching carrying capacity (K) 4 – Death  (Usually in experimental conditions when resources are used up)

Density-dependent selection or K-selected species These species are sensitive to population density they have few offspring, but provide extra parental care In density-dependent populations, birth rates fall and death rates rise with population density Density dependent limiting factors are those which limit the population only when large numbers of individuals present This is true for any resources which must be shared: food, nesting sites, diseases which are easily spread. These species thrive in populations living at or near the carrying capacity, where there is strong competition between individuals (like us!)

Examples: mammals, birds

Density-independent selection or r-selected species Density Independent factors always reduce the population size, regardless of how many individuals are present. These include natural disasters such as flood, fires, and earthquakes. Birth rate and death rate do not change with population density with density independent factors! Density-Independent Populations While most populations survive best at or near carrying capacity (K-selected species), some populations survive best well below carrying capacity  this helps maximize their reproduction! These organisms (r –selected) thrive: - when there is little competition - often found in disturbed habitats where organisms can be opportunistic (like…bacteria!)

Mechanisms of Density-Dependent Population Regulation Density-dependent birth and death rates are an example of negative feedback that regulates population growth Density-dependent birth and death rates are affected by many factors, such as competition for resources, territoriality, disease, predation, and accumulation of toxic wastes

a. Competition for Resources As population density increases, many density-dependent mechanisms slow or stop population growth: a. Competition for Resources In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate b. Toxic Wastes Accumulation of toxic wastes can contribute to density-dependent regulation of population size During fermentation, yeast uses carbohydrates to produce ethanol in wine making. The ethanol is toxic to yeasts and contributes to density dependent regulation. The alcohol content of wine is usually less than 13% because that is the maximum concentration of ethanol that yeast can tolerate.

c. Predation As a prey population builds up, predators may feed preferentially on that species “Boom & Bust Population Cycles” Some populations go through repeated and regular periods of boom followed by bust. This graph shows the 10-year cyclical fluctuations in the populations of the varying hare ("snowshoe rabbit") and its chief predator, the lynx, from 1850 to 1910. The size of the lynx population was closely dependent on the size of its prey (hare) population. The factors causing the hare population to go through its boom-and-bust cycles are still debated, but predation by lynxes was probably only one factor.

e. Territoriality f. Disease In many vertebrates and some invertebrates, competition for territory may limit density - Cheetahs use a chemical marker in urine to warn other cheetahs of their boundaries. f. Disease Population density can influence the health and survival of organisms In dense populations, pathogens can spread more rapidly

Population Dynamics The study of population dynamics focuses on the complex interactions between biotic and abiotic factors that cause variation in population size Changes in a species population affects other species, including our own 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 The global population is more than 6.8 billion people Though the global population is still growing, the rate of growth began to slow during the 1960s Annual percent increase 2009 Projected data 1950 1975 2000 2025 2050 Year

Currently, the population grows by more than 200, 000 people/ day! The human population is no longer growing exponentially but is still increasing rapidly No population can grow indefinitely, and humans are no exception The human population increased relatively slowly until about 1650 and then began to grow exponentially The Plague Human population (billions) 8000 BCE 4000 2000 CE 1000 3000 7 6 5 4 3 2 1 Currently, the population grows by more than 200, 000 people/ day!

Global Carrying Capacity How many humans can the biosphere support? Population ecologists predict a global population of 7.810.8 billion people in 2050 Estimates of Carrying Capacity The carrying capacity of Earth for humans is uncertain The average estimate is 10–15 billion The greatest crisis facing humans today is probably HUMAN POPULATION GROWTH! © 2011 Pearson Education, Inc.

Limits on Human Population Size The ecological or carbon footprint concept summarizes the combined land and water area needed to sustain the people of a nation (This includes land/ water needed to produce all the resources it consumes and absorb all the waste it generates) It is one measure of how close we are to the carrying capacity of Earth Countries vary greatly in footprint size and available ecological capacity Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes Unlike other organisms, we can regulate our population growth through social changes © 2011 Pearson Education, Inc.

Annual energy used per person around the world Gigajoules Figure 53.26 Annual per capita energy use around the world. > 300 150–300 50–150 10–50 < 10 To give you an idea, leaving a 100-watt light bulb on continuously for for one year would use 3.15 GJ 23

HOW CAN WE ALL HELP TO REDUCE OUR CARBON FOOTPRINT?! Turn it off  Turn off lights, televisions, videos, stereos and computers when not in use - they can use 10 to 40% of the power when on standby. Also, unplug chargers as soon as they have finished charging. Be exact  Use only as much water as you need. Close it  Don't leave fridge doors open for longer than necessary. Check your tires Properly inflated tires can improve your car’s fuel efficiency. Use no plastic  Use cloth bags when going shopping and avoid buying products which use too much plastic. Fan up  Instead of using air conditioners in the summer, wear cool clothes, and use a fan.

Drive less  Do your weekly errands in a single trip or pay your bills online. Walk, bike, ride the bus or carpool. Optimize your speed  You will consume up to 25% less fuel if you drive no more than 55 mi/hr. Drive hybrid  A hybrid or other fuel-efficient car emits less carbon dioxide. Use other energy sources  wind turbines, solar panels Replace them  Replace your incandescent bulb with a compact fluorescent light bulb (CFL). CFLs cost 3 to 5 times as much but use less than a third of the power. Also, replace old fridge and other appliances with energy-efficient ones. Recycle  Consume less, and re-use old products.