Population size and Conservation TEST 1 Mean = 83, Geometric mean = 82, Harmonic mean = 81, Median = 85. I will add tonight the grades to Blackboard (and also add key on Tu/We) Determining whether a population is growing or shrinking To get the test back you Predicting future population size need to see me in my office DSL 150-T. Non-genetic risks of small populations I am in my office: Tu 10-12, 3-5:30 Population Viability Analysis (PVA) Definitions PVA = Use of quantitative methods to evaluate and predict the likely future status of a population Use of quantitative methods to Status = likelihood that a population will be evaluate and predict the likely above a minimum size future status of a population Minimum size, quasi-extinction threshold = number below which extinction is very likely due to genetic or demographic risks Uses of PVA Assessment Assessing risk of a single population (for example Grizzly population) NPS Photo
Grizzly population size in Yellowstone national park Grizzlies are listed as threatened 1975; less than 200 bears left in Yellowstone 1983 Grizzly Bear recovery area (red) Increase of protection area discussed (blue) Uses of PVA Assessment Assessing risk of a single population (for example Grizzly population) Comparing risks between different populations Sockeye and Steelhead catch 1866 1991
Uses of PVA Assessment Assessing risk of a single population (for example Grizzly population) Comparing risks between different populations Analyzing monitoring data – how many years of data are needed to determine extinction risk? Example: Gray Whale Gray Whale How many data points do we need? 5 years? 10 years? 15 years? Gerber, Leah R., Douglas P. Demaster, and Peter M. Kareiva* 1999. Gray Whales and the Value of Monitoring Data in Implementing the U.S. Endangered Species Act. Conservation Biology 13:1215-1219. Uses of PVA Assessment Identify best ways to manage. Example: loggerhead turtles
Uses of PVA PVA indicates minimum of 2,500 km 2 needed to sustain population Assessment Identify best ways to manage. Example: loggerhead turtles Determine necessary reserve size. Example: African elephants Uses of PVA Assessment Assisting management Identify best ways to manage. Example: loggerhead turtles Determine necessary reserve size. Example: African elephants Determine size of population to reintroduce Example: European beaver Uses of PVA Assessment Assisting management Identify best ways to manage. Example: loggerhead turtles Determine necessary reserve size. Example: African elephants Determine size of population to reintroduce Example: European beaver Set limit to harvest (intentional and unintentional)
Uses of PVA Uses of PVA Assessment Assisting management Assessment Identify best ways to manage. Example: loggerhead turtles Assisting management Determine necessary reserve size. Identify best ways to manage. Example: African elephants Example: loggerhead turtles Determine size of population to reintroduce Determine necessary reserve size. Example: European beaver Example: African elephants Set limit to harvest (intentional and unintentional) Determine size of population to reintroduce Intentional harvest Example: European beaver Habitat degradation Set limit to harvest (intentional and unintentional) Intentional Harvest and By-Catch By-catch How many populations do we need to protect? Habitat degradation The Saga of the Furbish Lousewort Kate Furbish was a woman who, a century Types of PVA ago, Discovered something growing, and she classified it so That botanists thereafter, in their reference volumes state, That the plant's a Furbish lousewort. See, they named it after Kate. There were other kinds of louseworts, but the Furbish one was rare. It was very near extinction when they found out it was there. And as the years went by, it seemed, with ravages of weather, The poor old Furbish lousewort simply vanished altogether. But then in 1976, our bicentennial year, Furbish lousewort fanciers had some good news they could cheer. For along the Saint John River, guess what somebody found? Two hundred fifty Furbish louseworts growing in the ground. Now, the place where they were growing, by the Saint John River banks, Is not a place where you or I would want to live, no thanks. For in that very area, there was a mightty plan, An engineering project for the benefit of man. The Dickey-Lincoln Dam it's called, hydroelectric power. Energy, in other words, the issue of the hour. Make way, make way for progress now, man's ever-constant urge. And where those Furbish louseworts were, the dam would just submerge. The plants can't be transplanted; they simply Count based PVA: simple -- uses census data (head counts) wouldn't grow. Conditions for the Furbish louseworts have to be just so. And for reasons far too deep for me to know to explain, The only place they can survive is in that part of Structured PVA: uses demographic models (age structure) Maine. So, obviously it was clear that something had to give, And giant dams do not make way so that a plant can live. But hold the phone, for yes, they do. Indeed they Dickey-Lincoln Dam was too laden with must in fact. There is a law, the Federal Endangered Species ecological and economic problems to ever be Act, And any project such as this, though mighty and built, and the Furbish lousewort has held its exalted, If it wipes out threatened animals or plants, it own along the ice-scoured banks of the Saint must be halted. And since the Furbish lousewort is endangered John. In 1989 the U.S. Fish and Wildlife Service reported finding 6,889 flowering stems--far as can be, They had to call the dam off, couln't build it, more than the 250 or so that were thought to don't you see. For to flood that louseworth haven, where the exist earlier. Pedicularis furbishiae, a species Furbishes were at, Would be to take away their only extant habitat. with close relatives in Asia but nowhere else in And the only way to save the day, to end this North America, is still endangered, however. awful stall, Would be to find some other louseworts, anywhere at all. And sure enough, as luck would have it, strange The current threats are new dam proposals, logging, and real-estate development though it may seem, They found some other Furbish louseworts growing just downstream. Four tiny little colonies, one with just a single plant. PVM: Count based model N t = λ N t − 1 population size at time t- 1 population size at time t ‘lambda’ = growth rate includes birth and death does not include gene flow (movement among different populations)
Predicting What does mean λ future population sizes N t = λ N t − 1 N 1 = λ N 0 Population is shrinking λ < 1 Population is stable N 2 = λ N 1 = λ ( λ N 0 ) = λ 2 N 1 λ = 1 Population is growing λ > 1 N t = λ t N 0 Example N t = λ t N 0 Measuring � from data If we known the population size in two generations we are For some insect, � =1.2 and N0 = 150 able to calculate the growth rate How many insects will we have in 10 years? N t N10 � = � 150*1.2*1.2*1.2*1.2*1.2*1.2*1.2*1.2*1.2*1.2 λ = N t − 1 ������� = � 150 * 1.210 ������� = � 150 * 6.19 ������� = �� 929 Incorporating stochasticity into Stochasticity model Cyclical example Cyclical example � � For some insect, good = 1.3, bad = 1.1 and N0 = 150 With no variability of � ( = 1.2) Assume good/bad years alternate. N 10 = 929 With variability of � N 10 = 897 How many insects will we have in 10 years? ( � good = 1.3, � bad = 1.1) N10 = 150*1.1*1.3*1.1*1.3*1.1*1.3*1.1*1.3*1.1*1.3 Influence of small � is larger ������ = 897
Stochasticity Stochasticity N 0 = 150 N 0 = 150 � � 1 . 3 with p = 0 . 5 1 . 3 with p = 0 . 5 λ = λ = 1 . 1 with p = 0 . 5 1 . 1 with p = 0 . 5 N 10 = 150 × 1 . 1 × 1 . 1 × 1 . 3 × 1 . 3 × 1 . 1 × 1 . 1 × 1 . 1 × 1 . 1 × 1 . 1 × 1 . 3 = 642 N 10 = 150 × 1 . 1 × 1 . 1 × 1 . 3 × 1 . 3 × 1 . 1 × 1 . 1 × 1 . 1 × 1 . 1 × 1 . 1 × 1 . 3 = 642 N 10 = 150 × 1 . 1 × 1 . 1 × 1 . 3 × 1 . 3 × 1 . 1 × 1 . 1 × 1 . 3 × 1 . 1 × 1 . 3 × 1 . 3 = 897 N 10 = 150 × 1 . 1 × 1 . 1 × 1 . 3 × 1 . 3 × 1 . 1 × 1 . 1 × 1 . 3 × 1 . 1 × 1 . 3 × 1 . 3 = 897 Stochasticity Mean � = 1 Population Density (Ln) Models without a stochastic component produce ONE population size Models with a stochastic component produce a distribution of possible population sizes TIME Measuring � from data Distribution of population sizes Population size frequency If we known the population size in two generations we are 400 able to calculate the growth rate Population size 350 300 250 N t 200 λ = 150 N t − 1 100 50 0 0 1 2 3 4 5 6 7 8 9 10
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