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LIFE HISTORY AND HARVESTING READINGS: FREEMAN, 2005 Chapter 52 Pages 1206-1213 Chapter 54 Pages 1277-1283 ENDANGERED AND THREATENED SPECIES Endangered means a species that is in danger or extinction throughout all or a significant portion of its range.

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life history and harvesting



Chapter 52Pages 1206-1213

Chapter 54Pages 1277-1283

endangered and threatened species
  • Endangered means a species that is in danger or extinction throughout all or a significant portion of its range.
  • Threatened means a species that is likely to become endangered within the foreseeable future throughout all or a significant portion of its range.
  • The Endangered Species Act (EAS) was passed in 1973 to protect listed species for the “esthetic, ecological, educational, recreational, and scientific value to our Nation and its people”.
wildlife refuges and wilderness areas
  • In addition to the National Parks, Federal public lands include National Wildlife and Wilderness Areas that act to provide habitat for threatened and endangered species.
  • Of the 700 million acres (about 1/3 of the US), that are in the public domain about 170 million are devoted to this preservation effort.
larger preserves provide greater protection against extinction
Larger Preserves Provide Greater Protection Against Extinction
  • A study has followed mammal extinctions in National Parks in the US and Canada.
  • Species loss in 14 western North American National Parks is consistent with the species area relationships seen earlier.
  • Number of extinctions was greatest in smallest parks.

Newmark, 1987

changing survivorship as a management tool
  • Age specific mortality and natality data can be used to make management decisions in harvesting or conserving wildlife populations.
  • Assume that a population of interest is growing at too high a rate, what are the consequences of harvesting old versus young individuals on changing the rate of population growth?
managing a gray squirrel population
  • This squirrel population living in an Ohio woodlot has a type II survivorship curve.
  • Typical of a population with accidental death.
managing a gray squirrel population8
  • Squirrel populations begin reproduction at the end of the first year and continues throughout life.
  • The average number of offspring produced decreases with age.
what will happen if all squirrels 2 years and older are harvested13
What will happen if all squirrels 2 years and older are harvested?

All the squirrels you can eat and more!!!!

how to establish a squirrel preserve
How to establish a squirrel preserve?

Reduce survivorship of 1 year old squirrels to about 1/2 the original value and establish a new age distribution.

how to establish a squirrel preserve15
How to establish a squirrel preserve?

Reduce survivorship of 1 year old squirrels to about 1/2 the original value and establish a new age distribution.

managing populations within reserves a case study
Managing Populations Within Reserves: A Case Study
  • The Nature Conservancy in Scotland purchased an overgrazed isle with the goal of restoring the vegetation. The sheep were removed and the red deer population was hunted to remove 1/6 of adults after each spring census.
  • Is the level of Hunting:

1) high enough to prevent overgrazing by deer?


2) too high so as to result in extinction of red deer?

managing a red deer population
Managing A Red Deer Population
  • Recall that we found out that knowing something about the demography of a population would allow one to predict if the population was growing, declining or more or less stationary.
  • Records of survivorship and reproduction should allow us to answer these questions.
  • Survivorship of a cohort of female red deer and age specific births for the herd gave the following results:
demography of the red deer population20
Demography of the Red Deer Population
  • With Ro = 0.889, harvesting deer at this rate will result in a slow decline of the population. If allowed for a long period of time the vegetation will do fine, but eventually the red deer population would go locally extinct.
  • Thus hunting will have to be decreased slightly. One way would be to restrict hunting to those females over 3 years old and harvest 1/6 of the population over that age.
managing populations without over harvesting is a challenge
Managing Populations Without Over Harvesting Is A Challenge
  • Humans still harvest ocean populations of fish. Many of these fish stocks have been over fishes.
  • By applying sound principles of ecological management it should be possible to fish for many generations.
  • Remember harvesting is OK if Ro > 1.00.
harvest the oldest 3 age classes
Harvest The Oldest 3 Age Classes?

Ro = 0.60 Population declines

harvest 1 2 of the 3 oldest age classes
Harvest 1/2 Of The 3 Oldest Age Classes?

Ro = 1.02 Population stationary; harvest for all time.

sound management practices for natural populations
Sound Management Practices For Natural Populations
  • In managing natural populations it is important to understand basic principles of demography, control potential competitors or predators or pathogens and monitor population dynamics.
  • Also, recognize that small populations are particularly vulnerable to environmental changes.
population viability analysis
Population Viability Analysis
  • This is a model that estimates the likelihood that a population will avoid extinction for a given period of time.
  • Freeman (2005, page 1210) describes how it was used to manage an endangered marsupial population in Australia.
population viability analysis for an elephant population
Population Viability Analysis For An Elephant Population

A population viability analysis was conducted to answer the question:

How Large Should An Elephant Reserve Be?

how large should an elephant reserve be
How Large Should An Elephant Reserve Be?


  • Survivorship in normal years is known and can be estimated for 3 drought regimes.
  • 2) Age to first reproduction and calving interval is density dependent.
  • 3) Extinction occurs when N = 0 or N is all the same sex.
female survivorship in normal years
Female Survivorship in Normal Years

Results: Lifespan is around 60 years.Substantial “infant” mortality until large enough to avoid most predators (approximately 5 years). Type II survivorship up to about age 45 then rate increases.

projected population growth in normal years
Projected Population Growth in Normal Years

Results: Starting off with 11 males and 11 females with an r = 0.03 and living in an area of 4,000 square miles, the population leveled off at around 12,500 individuals in about 625 years.

probability of extinction
Probability of Extinction


1) If the reserve is 20 square mile the probability of extinction is 1 after only 250 years.

2) If the reserve is 200 square miles the probability of extinction is 0.1 after only 700 years.

3) If the reserve is 1,000 square miles the probably of extinction is 0.005 after 1,000 years.

how large should an elephant reserve be32
How Large Should An Elephant Reserve Be?

Conclusion: At a maximum population growth rate of 3% per year and a density of 3.1 elephants per square mile, a minimum reserve size of 1,000 square miles is necessary for a 99% probability of persistence for 1,000 years.

illinois is the prairie state
  • At the time of settlement, Illinois was dominated by grassland (prairie) communities.
  • With the invention of the mold-board plow by John Deer, a resident of Illinois, prairie was rapidly converted to farm field.
  • Today, less than 1/10 of 1% remains today.
nature preserves in northern illinois
Nature Preserves In Northern Illinois
  • The Chicago Region has a rich heritage of nature preserves.
  • The so called “Chicago Wilderness” occupies about 225,000 acres.
  • It includes around 106 nature preserves.
  • One can find out more about them by visiting:
  • Two of particular interest are Woodworth Prairie and Wolf Road Prairie.
cook county forest preserve

The Cook County Forest Preserve District consists of 67,000 acres (11% of county) acquired “for the purpose of protecting and preserving the flora, fauna and scenic beauties within such district, and to restore, restock, protect and preserve the natural forests and such lands together with their flora and fauna, as nearly as may be, in their natural state and condition.”

wolf road nature preserve
  • This 80 acre preserve is combination of three native community types: prairie, savanna, and wetlands.
  • It was too wet to plow or graze extensively and has survived as the largest black-soil prairie east of the Mississippi.
plant species at wolf road prairie
Plant Species at Wolf Road Prairie
  • These are less than 1% of the native plant species reported to live at Wolf Road Prairie (327 species).
  • An online tour of WRP is available by visiting:
life history and harvesting38



Chapter 52Pages 1206-1213

Chapter 54Pages 1277-1283