R/popgrow.R

In robertsaldivar/esm262package:

#' Population Growth Rate with Harvest
#'
#' This function determines the intrinsic population growth rate of a population, if that population is being harvested/hunted
#'.
#' @param growth rate is the rate the population grows, default = 0.05
#' @param carrying capacity is that the number of indiviuals of a population that a habitat can support, default = 2000
#' @param attack rate is the rate that hunters can attack and harvest an individual of the population, default = 0.05
#' @param handling time is the amount of time that it takes for a hunter to havest one individual before they they can harvest the next one, default = 0.2
#' @param population is the population size
#' @param hunters is the number of hunters harvesting the the population. To find th growth rate of the population with out harvest, set hunters to 0
#' @return is the intrinsic growth rate of the population at a given size with a give harvesting rate.
#' @author Robert Saldivar
#' @author Nathan BUrola
#'
#'
#' Assignment #1 Details
#' Include at least 2 inputs and several parameters (CHECK)
#' Add at least two different kinds of error checking (CHECK)
#' Add some error checking (at least 2 different kinds) (CHECK)
#' Save your function in a .R file (CHECK)
#' Adding comments to the function (CHECK)
#' In RMarkdown document, generate sample data for function in two different ways (CHECK)
#' Apply data to function (CHECK)
#' Graph and add some text describing how to interpret results
#'
popgrow = function(population, hunters, growth_rate=0.05, carrying_capacity = 3000, attack_rate = 0.05, handling_time = 0.2) {

  #make sure that population is not negative
  population = ifelse( (population < 0), return("population cannot be less than 0"), population )

  #make sure that # of hunter is not negative
  hunters = ifelse( (hunters < 0), NA, hunters)

  results = (growth_rate * population * (1 - population/carrying_capacity) - (hunters * (attack_rate * population)/(1 + attack_rate * handling_time * population)))

  return(results)
}