NRC 261 1st Edition Lecture 7 Outline of Last Lecture I Conditions of Wildlife Diseases II Disease Definition Continuum III Infectious Diseases IV Diseases in New England V Rabies a Raccoon Rabies in the Eastern U S b Raccoon Rabies in Pennsylvania c Raccoon Rabies Research d Rabies Vaccine e Landscape i Rural ii Urban iii Suburban f Trapping Protocol g Habitat Use Models Outline of Current Lecture I What Constitutes a Population II Population Dynamics III Population Change a Exponential Growth b Population Crashes IV Cyclic Population Change V Biological Carrying Capacity a Density independent factors b Density dependent factors VI Cultural Carrying Capacity VII Birth Reproductive Rates VIII Death Mortality Rates IX Original Questions Current Lecture population a group of individuals of a species for wild species it is meaningful to talk about its size how fast it grows how dense it is what its distribution is and other vital statistics characteristics that you want to describe a population by must be something that can be compared with other populations or with itself under 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 they would 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 seen at 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 American population 40 years ago yes because there were less than 50 in existence and they all lived in same areas so only one population since then because of conservation efforts there have been other crane populations established in other places now they re separate can t just be one continental population sometimes it can be every animal in a species sometimes just a few but it needs to have 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 to change 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 their population dynamics density physical distribution because food might differ reproduction differs etc would need to understand population dynamics within each of the places that they are found see why they re the same and why they re different comparison is key especially studying the different populations under specific circumstances Population Change exponential growth ex for a period of time nobody dies A pair of animals produce 2 offspring and those 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 10 organisms 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 an exponential 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 in 1907 when game reserve established back then the protocol was to kill all of the predators When that mortality factor disappeared the population had an exponential increase because they weren t dying of predation when a place goes from 4 00 deer to 100 000 deer in the same place things change one of those things was deer food disappearing much faster and some deer didn t get food population crashed they stopped reproducing more animals died and got down to around 10 000 animals can happen to populations when unchecked exponential growth occurs a balance of nature 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 that had never been eaten by caribou before now 6 000 animals and then the population crashed down to 42 caribou shows that there can be limits to population under weird circumstances non naturally 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 density gets higher supposedly there is some level that is reached that can support only that certain many animals and any more animals in that area will just send the population back to square one population grows relatively speaking and there s a point at which an environment can only regularly support a certain amount of animals and then the populations levels 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 is exponential growth once we reach around 9 10 billion if we maximize food production on earth the earth could support 10 billion people but if we shoot up more than that the earth will 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 during course of 80 years about every 10 years peak in the of snowshoe hares whose pelts were turned in and right about the same or a couple years after was a peak in the of lynx and then the population would crash looks like exponential growth and then a crash over and over again for both lynx and hares northern ecosystem few predators few prey few food items not very complex in general the chances increase that something will not be long term sustainable not many hares not many lynx because