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41 Cards in this Set
- Front
- Back
Is species conservation enough? |
focuses on single threatened species crisis approach to conservation should be complemented by bigger-picture approaches |
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Primary IUCN criteria for listing |
range size (small is worse) population abundance (small is worse) population trend (declining is worse) ongoing conservation efforts used to determine extinction risk |
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Population density affected by |
immigration and emigration births and deaths |
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What is a model? |
a simplified and abstracted representation of a system allows hypothesis testing and generalization |
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GEP box on models ---> |
all models are wrong but some are useful |
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Exponential growth model |
N(t+1) = N(t) + N(t)*r N(t) = N(0) * lambda(t) |
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Geometric rate of increase |
fundamental parameter in population ecology is the finite rate of increase of lambda |
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lambda (in the exponential growth model) |
describes the proportional increase (or decrease) in a population per time step |
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Did lambda apply to humans? |
yes |
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lambda < 1 means |
decline and eventual extinction |
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lambda = 1 means |
stable population |
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lambda > 1 means |
the population is growing |
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Why models are important for conservation |
assessment of extinction risk summarizes what is known about a population allows projections into the future assumptions are made explicit model can be refined as amore data become available model parameters can be compared among species and populations |
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Example of rates of decline |
Northwest Atlantic sharks |
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example of re-introduction |
muskox reintroduced to Nunivak Island, AK Census data collected to build a model in order to manage the population growth rates averages at lambda = 1.148 |
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Next step for the models? |
include real-world variability and uncertainty |
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So far models have assumed what? |
that species grow in a simple, predictable fashion assumed that growth parameters are fixed |
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deterministic model |
N(t+1) = N(t) * lambda when growth parameters are fixed |
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stochastic model |
N(t+1) = N(t) * lambda(t) takes into account that parameters vary widely more realistic |
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Causes of variability |
1. natural - population variability and environmental variability 2. sources of uncertainty - parameter uncertainty - model uncertainty - ignorance and surprises |
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What does stochastic models include |
both variability and uncertainty |
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Persistence vs. initial population |
can calculate probability of extinction (using same model) within 100 time steps |
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Environmental variability sources of environmental variation |
temporal spatial extreme |
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temporal variation |
light, temperature, rainfall, predation, food supply, etc. |
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spatial variation |
along depth gradients, across continents |
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extreme variation |
events or catastrophes - can harm or benefit |
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How do we incorporate environmental stochasticity |
assume that lambda caries over time through a statistical distribution |
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Muskox model where lambda = 1.148 and k = 500 density dependence: Ricker |
type: deterministic probability of extinction = 0 |
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Muskox model lambda = 1.148 and k = 500 |
type: stochastic (N=25) using demographic stochasticity N is how many many times the model is run the line is the mean and the data includes error as well as the highest and lowest value |
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same model but adding a standard deviation in lambda of 10% |
adds a lot of variability to the data |
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add a standard deviation in lambda of 30% |
trajectory summary means that the probability of extinction within 50 years is about 10% |
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Problem: parameters are always estimated, never known |
solution: use larger sample size, get additional information to reduce uncertainty |
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problem: models are a simplification of the real world |
solution: compare different models and see how their behaviour varies |
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Overall solution to redce uncertainty |
find a good compromise between simplification and realism |
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Allee effects |
correlation between population size or density and the mean individual fitness of a population or species |
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allee effects in great auk |
overhunting by museum collectors |
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allee effects in Napolean wrasse |
overfishing increased price |
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allee effects in passenger pigeon |
failure of large breeding colonies |
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urchin |
critical density needed for urchin fertilization succes |
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populations of most concern |
populations in rapid decline |
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stochastic models are used for.... |
to assess population variability and uncertainty |