NRC 261 1st Edition Lecture 7Outline of Last Lecture I. Conditions of Wildlife DiseasesII. Disease Definition & ContinuumIII. Infectious DiseasesIV. Diseases in New EnglandV. Rabiesa. Raccoon Rabies in the Eastern U.Sb. Raccoon Rabies in Pennsylvaniac. Raccoon Rabies Researchd. Rabies Vaccinee. Landscapei. Ruralii. Urbaniii. Suburbanf. Trapping Protocolg. Habitat Use ModelsOutline of Current LectureI. What Constitutes a PopulationII. Population DynamicsIII. Population Changea. Exponential Growthb. Population CrashesIV. Cyclic Population ChangeV. Biological Carrying Capacitya. Density independent factorsb. Density dependent factorsVI. Cultural Carrying CapacityVII. Birth/Reproductive RatesVIII. Death/Mortality RatesIX. Original QuestionsCurrent Lecturepopulation = a group of individuals of a species• for wild species it is meaningful to talk about its size, how fast it grows, how denseit is, what its distribution is, and other vital statistics (characteristics that you wantto describe a population by)• must be something that can be compared with other populations, or with itselfunder different circumstances• if it’s not meaningful to compare, then they aren’t populations• largely reproductively isolated from other populations of the same species• not common that those populations inter-breed with one another, otherwise theywould be one large population• they might inter-breed a little bit, a medium amount, or a lot• then it depends on the degree of isolation!What Constitutes a Population?• Robins—when you look out your window and see 20 on the lawn• is this a population? NOPE• they’re migratory animals, they spread out lots of places — the individuals seenat a given time don’t make up a population• Snapping Turtles in a lake — are they a population?!• possibly, depends on how many there are• 2 snapping turtles in the campus pond is just a pair of turtles• what about a dozen pairs of turtles with an isolated water system &interbreeding? YES, that could be a population• Ducks — the mallard duck population of North America? NO, too big• Whooping Crane — could you consider all whooping cranes in North Americanpopulation?• 40 years ago, yes because there were less than 50 in existence and they all livedin same areas (so only one population)• since then because of conservation efforts, there have been other cranepopulations established in other places — now they’re separate, can’t just beone continental population*sometimes it can be every animal in a species, sometimes just a few, but it needs tohave its own population characteristics, isolation etc.!Population Dynamics• the study of how and why populations change in numbers and distribution**one of the most important concepts**• How many are there? Where are they? What’s the mechanism for populations tochange (how do things vary from place to place, over time or over space)?!Little Brown Bat• for every distinctive population, they might be somewhat different in theirpopulation dynamics (density, physical distribution because food might differ,reproduction differs, etc.)• would need to understand population dynamics within each of the places that theyare found — see why they’re the same and why they’re different• -comparison is key, especially studying the different populations under specificcircumstances!Population Change!• *exponential growth• ex: for a period of time, nobody dies. A pair of animals produce 2 offspring, andthose animals all reproduce the next year (2 —>4 —> 8—>16 etc.)• this is an exponential curve• certain percentage increase that a population can attain (if you have 10organisms and they increase at 20% a year, then you’ll have 12 the next year)• possible to rapidly increase a population — there is a potential to grow at anexponential rate for all species (if nobody dies)!sometimes a population will increase exponentially, but then…Population Crashes• was a population of mule deer (in AZ), game preserve was established in this area in1907 (when game reserve established back then, the protocol was to kill all of thepredators). When that mortality factor disappeared, the population had anexponential increase because they weren’t dying of predation• when a place goes from 4,00 deer to 100,000 deer in the same place, thingschange — one of those things was deer food disappearing much faster and somedeer didn’t get food• population crashed, they stopped reproducing, more animals died and got down toaround 10,000 animals• can happen to populations when unchecked exponential growth occurs, a balance ofnature that was once there is suddenly nonexistent• caribou introduced onto an island where there had never been caribou (29 animals)• population increased exponentially, island had no predators and food supply thathad never been eaten by caribou before (now 6,000 animals) and then thepopulation crashed down to 42 caribou• shows that there can be limits to population under weird circumstances (nonnaturally evolved circumstances)!instead of exponential growth happening more often,Carrying Capacity!• Logistic (s-shaped) growth• as population density increases, relative food density goes down, and as the densitygets higher, supposedly there is some level that is reached that can support onlythat certain many animals, and any more animals in that area will just send thepopulation back to square one• population grows relatively speaking, and there’s a point at which an environmentcan only regularly support a certain amount of animals, and then the populationslevels out at around this number (increase per year slows down)• **this is what is expected/common among normal circumstance**!Human Population Growth?• Will it be an exponential increase and a crash, or a logistic curve? right now it isexponential growth• once we reach around 9-10 billion, if we maximize food production on earth, theearth could support 10 billion people, but if we shoot up more than that the earthwill run out of food and there will be a crash!Cyclic Population Change• relationship between snowshoe hares and lynx = the 10 year cycle• data set comes from counts of the number of furs of those animals traded duringcourse of 80 years• about every 10 years, peak in the # of snowshoe hares whose pelts were turnedin, and right about the same or a couple years after was a peak in the # of lynx,and then the population would