as <- runif(30)  # limit for
bs <- runif(30)
cs <- runif(30)  # distribution of food sources ('random'/'clustered')

p_space <- list ()
for (a in as){
  for (b in bs){
    for (c in cs){
      p_space[[length(p_space)+1]] <- c(a,b,c)
    }
  }
}
made_up <- function(pvec){
  a <- pvec[1]
  b <- pvec[2]
  c <- pvec[3]
  for(i in 1:10000){
    d <- a*b*c
  }
  return(list(a,b,c,d))
}
system.time({
  z <- lapply(p_space,made_up)
  results1 <- data.frame(matrix(unlist(z),ncol = 4, byrow = T))
  colnames(results1) <- c('a','b','c','product')

})

 user  system elapsed
  21.23    0.01   21.26

library(parallel)
no_cores <- detectCores()
cl <- makeCluster(no_cores)
clusterExport(cl, c("p_space"))
# clusterEvalQ() #for libraries on all nodes
system.time ({
  z <- parLapply(cl, p_space, made_up)
  results <- data.frame(matrix(unlist(z),ncol = 4, byrow = T))
  colnames(results) <- c('a','b','c','product')
})

user  system elapsed
   0.02    0.02   10.86