11 Comparing diet data to previous studies

Using data compiled by Sherratt et al. (2018)

require(tidyverse)

sherratt <- read.csv("Data/Sea snake diet data_Sherratt et al_2018.csv")

gc <- read.csv("Data/Sea_snakes_gut_content_2018-19.csv")

diet <- gc %>%
    filter(Source == "Gut content", Snake.Species %in% c("Hydrophis schistosus", "Hydrophis curtus"), Prey.Family != "") %>%
    group_by(Snake.Species, Prey.Family) %>%
    summarise(Prey.count = length(unique(GC.Code)), Location = "India", References = "Dsouza et al. 2021") %>%
    ungroup() %>%
    rename(Snake.binomial = Snake.Species) %>%
    full_join(sherratt)

11.1 Sample size

diet %>%
    group_by(Snake.binomial) %>%
    summarise(N = sum(Prey.count), n.studies = length(unique(References)), n.locations = length(unique(Location)))

Snake.binomial	N	n.studies	n.locations
Hydrophis curtus	280	3	3
Hydrophis schistosus	260	2	2

11.2 Prey family richness by region

diet %>%
    group_by(Snake.binomial, Location) %>%
    summarise(Richness = length(unique(Prey.Family)), N = sum(Prey.count))

Snake.binomial	Location	Richness	N
Hydrophis curtus	Australia	18	118
Hydrophis curtus	India	10	32
Hydrophis curtus	Malaysia	33	130
Hydrophis schistosus	India	13	88
Hydrophis schistosus	Malaysia	9	172

11.3 Prey Preference by location

prey_loc <- diet %>%
    dplyr::select(Snake.binomial, Location, Prey.Family, Prey.count) %>%
    group_by(Snake.binomial, Location) %>%
    mutate(Total.Prey.Count = sum(Prey.count)) %>%
    group_by(Snake.binomial, Location, Prey.Family) %>%
    summarise(prop = sum(Prey.count)/Total.Prey.Count) %>%
    distinct(Prey.Family, .keep_all = T) %>%
    mutate(Prey.Family = ifelse(Prey.Family %in% c("Infraclass Teleost", "Unidentified"), "Unidentified Teleost", Prey.Family))

11.3.1 H. curtus

prey_loc %>%
    filter(Snake.binomial == "Hydrophis curtus") %>%
    ggplot(aes(reorder(Prey.Family, -prop), prop)) + geom_col(col = "black", width = 0.5) + labs(x = "Prey Family", y = "Proportion") + theme(axis.text.x = element_text(angle = 60, 
    hjust = 1, face = "italic")) + facet_wrap(~Location, scales = "free_y", ncol = 1)

ggsave(last_plot(), filename = "./Figures and Tables/figD1.png", height = 13.5, width = 16)

11.3.2 H. schistosus

prey_loc %>%
    filter(Snake.binomial == "Hydrophis schistosus") %>%
    ggplot(aes(reorder(Prey.Family, -prop), prop)) + geom_col(col = "black", width = 0.5) + labs(x = "Prey Family", y = "Proportion") + theme(axis.text.x = element_text(angle = 60, 
    hjust = 1, face = "italic")) + facet_wrap(~Location, scales = "free_y", ncol = 1)

ggsave(last_plot(), filename = "./Figures and Tables/figD2.png", height = 9, width = 16)