HOMEWORK #3: RHINO PVA
Assignment: Use the VORTEX program and the following field data (modified from U. Seal & T. Foose, CBSG Javan Rhinoceros PVA, 1989) to model the probability of extinction of the Ujong Kulon Reserve population of rhinoceros in Java. Run 10 simulations for 100 years each. Record your input and output values on copies of the Input and Output Data Sheets. Input and Output Data Sheets are due Wednesday, April 4.
Field Data: The Javan rhino exists in the wild as a single population in Ujong Kulon Reserve. The population currently consists of 64 animals and has not increased in the past 10-12 years. The reason for the limited recruitment is not understood. Inbreeding is thought to be affecting birth rates and juvenile survival. This assumption is supported by observation of high rates of abnormal sperm relative to that in larger populations. A genetic analysis suggests that there is a large number of recessive lethal alleles in the population.
Adult rhinos reproduce only once each year, producing a single offspring/litter. On average, the sex ratio of offspring is 1:1. The age of first reproduction is about 5 years for both sexes. However, in an average year only 1 out of 3 adult females successfully bear offspring. Reproduction by females is susceptible to environmental variation, and the 95% CI of successful female reproduction ranges from 1 out of 6 to 3 out of 6 females. These rhinos have a polygamous mating system, with all males in the breeding pool.
Mortality rates for infants (age 0 - 1) of both sexes is high (20%) due to disease and accidents (SD = 5%). The mortality rate for juveniles of both sexes drops to 5% (SD = 1.5%) for all subsequent age intervals. The mortality rate for adult females (> 5 years old) is 4% each year (SD = 1%), largely as a result of senescence. The mortality rate for adult males is higher (8%, SD = 2%) because of male-male fighting and poaching for horn. Note that the above mortalities are age-specific mortalities, not survivorship. The maximum age for both sexes is 35 yrs.
The Ujong Kulon Reserve can sustain up to 75 rhinos. It is protected by law and not expected to increase in size or quality in the near future.
Disease is the only potential catastrophe threatening the Reserve population. Outbreaks of disease may kill up to 25% of the population (severity with respect to survival = 0.75), but do not have an impact on reproduction. There is an 8% probability of disease affecting the population in any given year.
The age structure of the current population was determined by censuses as:
Age |
Males |
Females |
1 |
2 |
2 |
2 |
1 |
3 |
3 |
2 |
1 |
4 |
3 |
2 |
Adults > 5 yrs: 23 males, 25 females. Total population size: 64 individuals
Fill out your answers on the datasheet provided and supplement with one (and only one) paragraph of text if you feel the need.
Optional: If you have the time, go beyond the homework and see what it takes to make the rhinos survive as a viable population for 100 years. Which variables have the biggest impact? Are any of these variables ones that you might be able to change realistically as a manager of a rhino reserve? Thinking about this will help you with your term paper...