distr = function(type,param,pool_size) {
# This function generates some abundance distributions 
# It returns proportions of abundances

no_rep = 100;  # constant

#type = 1 geometric (param is the proportion of neighbouring species)
#     = 2 lognormal (param is the standard deviation)
#     = 3 Tokeshi power fraction
#     = 4 broken stick (fully random)

  if (type == 1) {
    #geometric 
    abund = NULL
    abund[1]= param;
    for (i in 2:pool_size) 
      abund[i] = abund[i - 1] * param 
  }

  if (type == 2) { 
  #lognormal 
     xabund=NULL
     abund=rep(0,pool_size)
     for (k in 1:no_rep) {
        for (i in 1:pool_size) {
           sd = rnorm(1);
           xabund[i] = exp(param * sd);
        }
        xabund = sort(xabund, decreasing=T)
        abund = abund + xabund             
     }
     abund = abund / no_rep;
  }

  if (type == 3) {
  #broken stick
     abund=rep(0,pool_size)
     for (k in 1:no_rep) {
        xabund = 1
        for (i in 1:(pool_size-1)) {
           s=length(xabund)
           r=ceiling(s * runif(1))
           r1=runif(1);
           xabund[r] = xabund[r] * r1
           xabund=c(xabund, xabund[r] * (1-r1))
        }
        xabund = sort(xabund, decreasing=T)
        abund = abund + xabund             
     }
     abund = abund / no_rep
  }

  if (type ==4) {
  #random
     abund=rep(0,pool_size)
     for (k in 1:no_rep) {
        xabund = runif(pool_size);
        xabund = sort(xabund, decreasing=T)
        abund = abund + xabund;              
     }
     abund = abund / no_rep;
  
  }

 abund=abund/sum(abund)
 #n=cumsum(abund);
 abund
}