Joel H. Nitta
04 October, 2022Source:
CANAPE stands for “Categorical Analysis of Neo- And Paleo-Endemism”, and provides insight into the evolutionary processes underlying endemism (Mishler et al. 2014). The idea is basically that endemic regions may be so because either they contain range-restricted parts of a phylogeny that have unusually long branch lengths (paleoendemism), or unusually short branch lengths (neoendemism), or a mixture of both. Paleoendemism may reflect old lineages that have survived extinctions; neoendemism may reflect recently speciated lineages that have not yet dispersed.
This vignette replicates the analysis of Mishler et al. 2014, where CANAPE was originally defined.
Start by loading
canaper and some other packages we will use for this vignette:
canaper package comes with the dataset used in Mishler et al. (2014). Let’s load the data into memory:
acacia dataset is a list including two items. The first,
phy, is a phylogeny of Acacia species in Australia:
acacia$phy #> #> Phylogenetic tree with 510 tips and 509 internal nodes. #> #> Tip labels: #> Pararchidendron_pruinosum, Paraserianthes_lophantha, adinophylla, semicircinalis, aphanoclada, inaequilatera, ... #> #> Rooted; includes branch lengths.
comm, is a community dataframe with species as columns and rows as sites. The row names (sites) correspond to the centroids of 50 x 50 km grid cells covering Australia. The community matrix is too large to print out in its entirety, so we will just take a look at the first 8 rows and columns1:
dim(acacia$comm) #>  3037 508 acacia$comm[1:8, 1:8] #> abbreviata acanthaster acanthoclada acinacea aciphylla acoma #> -1025000:-1825000 0 0 0 0 0 0 #> -1025000:-1875000 0 0 0 0 0 0 #> -1025000:-1925000 0 0 0 0 0 0 #> -1025000:-1975000 0 0 0 0 0 0 #> -1025000:-2025000 0 0 0 0 0 0 #> -1025000:-2075000 0 0 0 0 0 0 #> -1025000:-2125000 0 0 0 0 0 0 #> -1025000:-2225000 0 0 0 0 0 0 #> acradenia acrionastes #> -1025000:-1825000 0 0 #> -1025000:-1875000 0 0 #> -1025000:-1925000 0 0 #> -1025000:-1975000 0 0 #> -1025000:-2025000 0 0 #> -1025000:-2075000 0 0 #> -1025000:-2125000 0 0 #> -1025000:-2225000 0 0
There are many metrics that describe the phylogenetic diversity of ecological communities. But how do we know if a given metric is statistically significant? One way is with a randomization test. The general process is:
- Generate a set of random communities
- Calculate the metric of interest for each random community
- Compare the observed values to the random values
Observed values that are in the extremes (e.g, the top or lower 5% for a one-sided test, or either the top or bottom 2.5% for a two-sided test) would be considered significantly more or less diverse than random.
The main purpose of
canaper is to perform these randomization tests.
canaper generates random communities using the
vegan package. There are a large number of pre-defined randomization algorithms available in
vegan2, as well as an option to provide a user-defined algorithm. Selecting the appropriate algorithm is not trivial, and can greatly influence results3. For details about the pre-defined algorithms, see
This example also demonstrates one of the strengths of
canaper: the ability to run randomizations in parallel4. This is by far the most time-consuming part of CANAPE, since we have to repeat the calculations many (e.g., hundreds or more) times across the randomized communities to obtain reliable results. Here, we set the number of iterations (
n_iterations; i.e., the number of swaps used to produce each randomized community) fairly high because this community matrix is large and includes many zeros; thorough mixing by swapping many times is required to completely randomize the matrix.
We will use a low number of random communities (
n_reps) so things finish relatively quickly; you should consider increasing
n_reps for a “real” analysis5. We will use the
curveball randomization algorithm, which maintains species richness and abundance patterns while randomizing species identity (Strona et al. 2014)6.
# Set a parallel back-end, with 2 CPUs running simultaneously plan(multisession, workers = 2) # Uncomment this to show a progress bar when running cpr_rand_test() # progressr::handlers(global = TRUE) # nolint # Set a random number generator seed so we get the same results if this is # run again set.seed(071421) tic() # Set a timer # Run randomization test acacia_rand_res <- cpr_rand_test( acacia$comm, acacia$phy, null_model = "curveball", n_reps = 20, n_iterations = 100000, tbl_out = TRUE ) #> Warning in match_phylo_comm(phy = phy, comm = comm): Dropping tips from the tree because they are not present in the community data: #> Pararchidendron_pruinosum, Paraserianthes_lophantha toc() # See how long it took #> 49.352 sec elapsed # Switch back to sequential (non-parallel) mode plan(sequential)
Let’s take a peek at the output.
acacia_rand_res #> # A tibble: 3,037 × 55 #> site pd_obs pd_ra…¹ pd_ra…² pd_ob…³ pd_ob…⁴ pd_ob…⁵ pd_ob…⁶ pd_ob…⁷ pd_ob…⁸ #> <chr> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> #> 1 -102… 0.0145 0.0207 0.00432 -1.46 1 19 20 0.05 0.95 #> 2 -102… 0.0382 0.0522 0.00704 -1.99 0 20 20 0 1 #> 3 -102… 0.0378 0.0371 0.00535 0.130 12 8 20 0.6 0.4 #> 4 -102… 0.0570 0.0606 0.00758 -0.480 6 14 20 0.3 0.7 #> 5 -102… 0.0409 0.0423 0.00836 -0.176 11 9 20 0.55 0.45 #> 6 -102… 0.00998 0.0102 0.00206 -0.0890 11 9 20 0.55 0.45 #> 7 -102… 0.0187 0.0230 0.00378 -1.14 3 17 20 0.15 0.85 #> 8 -102… 0.0434 0.0516 0.00862 -0.955 4 16 20 0.2 0.8 #> 9 -102… 0.0111 0.0104 0.00172 0.418 17 3 20 0.85 0.15 #> 10 -102… 0.0903 0.0896 0.0114 0.0601 13 7 20 0.65 0.35 #> # … with 3,027 more rows, 45 more variables: pd_alt_obs <dbl>, #> # pd_alt_rand_mean <dbl>, pd_alt_rand_sd <dbl>, pd_alt_obs_z <dbl>, #> # pd_alt_obs_c_upper <dbl>, pd_alt_obs_c_lower <dbl>, pd_alt_obs_q <dbl>, #> # pd_alt_obs_p_upper <dbl>, pd_alt_obs_p_lower <dbl>, rpd_obs <dbl>, #> # rpd_rand_mean <dbl>, rpd_rand_sd <dbl>, rpd_obs_z <dbl>, #> # rpd_obs_c_upper <dbl>, rpd_obs_c_lower <dbl>, rpd_obs_q <dbl>, #> # rpd_obs_p_upper <dbl>, rpd_obs_p_lower <dbl>, pe_obs <dbl>, …
cpr_rand_test() produces a lot of columns. Here,
pd_obs is the observed value of phylogenetic diversity (PD). Other columns starting with
pd refer to aspects of the randomization:
pd_rand_mean is the mean PD across the random communities,
pd_rand_sd is the standard deviation of PD across the random communities,
pd_obs_z is the standard effect size of PD, etc.
For details about what each column means, see
The next step in CANAPE is to classify types of endemism. For a full description, see Mishler et al. (2014). In short, this defines endemic regions based on combinations of the p-values of phylogenetic endemism (PE;
pe_obs) and PE measured on an alternative tree with all branch lengths equal (
pe_alt). Here is a summary borrowed from the biodiverse blog, modified to use the variables as they are defined in
- If either
pe_alt_obsare significantly high then we look for paleo- or neo-endemism
rpe_obsis significantly high then we have palaeo-endemism
- Else if
rpe_obsis significantly low then we have neo-endemism
- Else we have mixed age endemism, in which case
- If both
pe_alt_obsare highly significant (p < 0.01) then we have super endemism (high in both paleo and neo)
- Else we have mixed (some mixture of paleo, neo and nonendemic)
- If both
- Else if neither
pe_alt_obsare significantly high then we have a non-endemic cell
A similar function to
cpr_classify_endem() is available to classify significance of the randomization test,
cpr_classify_signif(). Note that both of these take a
data.frame as input and return a
data.frame as output, so they are “pipe-friendly”. The second argument of
cpr_classify_signif() is the name of the biodiversity metric that you want to classify. This will add a column
*_signif with the significance relative to the random distribution for that metric. For example,
cpr_classify_signif(df, "pd") will add the
pd_signif column to
We can chain them together as follows:
acacia_canape <- cpr_classify_endem(acacia_rand_res) |> cpr_classify_signif("pd") |> cpr_classify_signif("rpd") |> cpr_classify_signif("pe") |> cpr_classify_signif("rpe") # Take a look at one of the significance classifications: table(acacia_canape$pd_signif) #> #> < 0.01 > 0.99 not significant #> 582 91 2364
With the randomizations and classification steps taken care of, we can now visualize the results to see how they match up with those of Mishler et al. (2014).
Note that the results will not be identical because we have used a different randomization algorithm from the paper and because of stochasticity in the random values, as well as fewer replicates for the randomization test.
Here is Figure 2, showing the results of the randomization test for PE, RPE, PE, and RPE:
# Fist do some data wrangling to make the results easier to plot # (add lat/long columns) acacia_canape <- acacia_canape |> separate(site, c("long", "lat"), sep = ":") |> mutate(across(c(long, lat), parse_number)) theme_update( panel.background = element_rect(fill = "white", color = "white"), panel.grid.major = element_line(color = "grey60"), panel.grid.minor = element_blank() ) a <- ggplot(acacia_canape, aes(x = long, y = lat, fill = pd_signif)) + geom_tile() + # cpr_signif_cols_2 is a CVD-friendly color palette in canaper scale_fill_manual(values = cpr_signif_cols_2, name = "Phylogenetic diversity") + guides(fill = guide_legend(title.position = "top", label.position = "bottom")) b <- ggplot(acacia_canape, aes(x = long, y = lat, fill = rpd_signif)) + geom_tile() + scale_fill_manual( values = cpr_signif_cols_2, name = "Relative phylogenetic diversity" ) + guides(fill = guide_legend(title.position = "top", label.position = "bottom")) c <- ggplot(acacia_canape, aes(x = long, y = lat, fill = pe_signif)) + geom_tile() + scale_fill_manual(values = cpr_signif_cols_2, name = "Phylogenetic endemism") + guides(fill = guide_legend(title.position = "top", label.position = "bottom")) d <- ggplot(acacia_canape, aes(x = long, y = lat, fill = rpe_signif)) + geom_tile() + scale_fill_manual( values = cpr_signif_cols_2, name = "Relative phylogenetic endemism" ) + guides(fill = guide_legend(title.position = "top", label.position = "bottom")) a + b + c + d + plot_annotation(tag_levels = "a") & theme(legend.position = "top")
And here is Figure 3, showing the results of CANAPE:
a <- ggplot(acacia_canape, aes(x = long, y = lat, fill = endem_type)) + geom_tile() + # cpr_endem_cols_4 is a CVD-friendly color palette in canaper scale_fill_manual(values = cpr_endem_cols_4) + guides( fill = guide_legend(title.position = "top", label.position = "bottom") ) + theme(legend.position = "bottom", legend.title = element_blank()) b <- ggplot( acacia_canape, aes(x = pe_alt_obs, y = pe_obs, color = endem_type) ) + geom_abline(slope = 1, color = "darkgrey") + geom_point() + scale_color_manual(values = cpr_endem_cols_4) + labs( x = "Phylogenetic endemism on comparison tree", y = "Phylogenetic endemism on actual tree" ) + theme_bw() + theme(legend.position = "none") a + b + plot_layout(ncol = 1) + plot_annotation(tag_levels = "a")