Calculate abundance, richness, and diversity from count data.
In the situation that some surveys had no birds observed, there will be no
entry in the avian_common_count
data set.
Thus, we combine this data set with the avian_surveys
data set to insure that
all surveys are represented.
The following step, which fills in zeros for any species not observed during a
particular survey, is unnecessary for calculation of abundance, richness, and
diversity but will likely be helpful for other tasks, e.g. abundance or
occupancy modeling.
library(dplyr) library(tidyr) library(STRIPSSchulte) all_counts <- avian_common_count %>% right_join(avian_surveys[,"survey"], by="survey") %>% # include surveys with no observations complete(survey, abbrev, fill = list(count=0)) # fill all missing survey-abbrev combinations with zero counts
The vegan package has functionality to calculate Shannon, Simpson, and inverse Simpson measures of diversity. For avian populations, we typically use inverse Simpson diversity, but there is an issue with defining diversity when no individuals of any species are observed. We propose (perhaps it is already used or there is a different solution) to define inverse Simpson diversity to be 0 when there are no individuals of any species observed.
diversity <- function(x) { div <- vegan::diversity(x, index = "inv") # Inverse Simpson's Diversity div[is.infinite(div)] <- 0 return(div) }
all_counts %>% group_by(survey) %>% summarize(abundance = sum(count), richness = sum(count>0), diversity = diversity(count))
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