douconca (version 1.2.3)

fN2: Hill number of order 2: N2

Description

Calculate Hill number N2.

Usage

fN2(x)

Value

scalar: Hill number N2.

Arguments

x

a numeric vector.

References

Hill,M.O. (1973). Diversity and evenness: a unifying notation and its consequences. Ecology, 54, 427-432. tools:::Rd_expr_doi("10.2307/1934352").

ter Braak, C.J.F. (2019). New robust weighted averaging- and model-based methods for assessing trait-environment relationships. Methods in Ecology and Evolution, 10 (11), 1962-1971. tools:::Rd_expr_doi("10.1111/2041-210X.13278").

Examples

data("dune_trait_env")

# rownames are carried forward in results
rownames(dune_trait_env$comm) <- dune_trait_env$comm$Sites
Y <- dune_trait_env$comm[, -1] # must delete "Sites"
Y_N2 <- ipf2N2(Y, updateN2 = FALSE, N2N_N2_species = FALSE)
attr(Y_N2, "iter") # 4

# show that column margins of the transform matrix are
# equal to the Hill N2 values
diff(range(colSums(Y_N2) / apply(X = Y, MARGIN = 2, FUN = fN2))) #  8.881784e-16
diff(range(rowSums(Y_N2) / apply(X = Y, MARGIN = 1, FUN = fN2))) #  0.07077207

Y_N2i <- ipf2N2(Y, updateN2 = TRUE, N2N_N2_species = FALSE)
attr(Y_N2i, "iter") # 5
diff(range(colSums(Y_N2i) / apply(X = Y_N2i, MARGIN = 2, FUN = fN2))) # 2.220446e-15
diff(range(rowSums(Y_N2i) / apply(X = Y_N2i, MARGIN = 1, FUN = fN2))) # 0.105742

# the default version:
Y_N2N_N2i <- ipf2N2(Y)
# ie. 
# Y_N2N_N2i <- ipf2N2(Y, updateN2 = TRUE, N2N_N2_species = TRUE)
attr(Y_N2N_N2i, "iter") # 16
N2 <- apply(X = Y_N2N_N2i, MARGIN = 2, FUN = fN2)
N <- nrow(Y)
diff(range(colSums(Y_N2N_N2i) / (N2 * (N - N2)))) # 2.220446e-16

N2_sites <- apply(X = Y_N2N_N2i, MARGIN = 1, FUN = fN2)
R <- rowSums(Y_N2N_N2i)
N * max(N2_sites / sum(N2_sites) - R / sum(R)) # 0.009579165

sum(Y_N2N_N2i) - sum(Y)

mod0 <- dc_CA(formulaEnv = ~ A1 + Moist + Mag + Use + Manure,
              formulaTraits = ~ SLA + Height + LDMC + Seedmass + Lifespan,
              response = Y,  
              dataEnv = dune_trait_env$envir,
              dataTraits = dune_trait_env$traits, 
              divide = FALSE,
              verbose = FALSE)

mod1 <- dc_CA(formulaEnv = ~ A1 + Moist + Mag + Use + Manure,
              formulaTraits = ~ SLA + Height + LDMC + Seedmass + Lifespan,
              response = Y_N2N_N2i,  
              dataEnv = dune_trait_env$envir,
              dataTraits = dune_trait_env$traits, 
              verbose = FALSE)

mod1$eigenvalues / mod0$eigenvalues
# ratios of eigenvalues greater than 1,
# indicate axes with higher (squared) fourth-corner correlation

# ipf2N2 for a presence-absence data matrix																   
Y_PA <- 1 * (Y > 0)
Y_PA_N2 <- ipf2N2(Y_PA, N2N_N2_species = FALSE)
attr(Y_PA_N2, "iter") # 1
diff(range(Y_PA - Y_PA_N2)) # 4.440892e-16, i.e no change

Y_PA_N2i <- ipf2N2(Y_PA, N2N_N2_species = TRUE)
attr(Y_PA_N2i, "iter") # 9
N_occ <- colSums(Y_PA) # number of occurrences of species
N <- nrow(Y_PA)
plot(N_occ, colSums(Y_PA_N2i))
cor(colSums(Y_PA_N2i), N_occ * (N - N_occ)) # 0.9916
mod2 <- dc_CA(formulaEnv = ~ A1 + Moist + Mag + Use + Manure,
              formulaTraits = ~ SLA + Height + LDMC + Seedmass + Lifespan,
              response = Y_PA,  
              dataEnv = dune_trait_env$envir,
              dataTraits = dune_trait_env$traits,
              divideBySiteTotals = FALSE,
              verbose = FALSE)
			  
mod3 <- dc_CA(formulaEnv = ~ A1 + Moist + Mag + Use + Manure,
              formulaTraits = ~ SLA + Height + LDMC + Seedmass + Lifespan,
              response = Y_PA_N2i,  
              dataEnv = dune_trait_env$envir,
              dataTraits = dune_trait_env$traits,
              verbose = FALSE)
			  
mod3$eigenvalues / mod2$eigenvalues
# ratios of eigenvalues greater than 1,
# indicate axes with higher (squared) fourth-corner correlation