Dietary preferences and feeding strategies of Colombian highland woolly monkeys

Abstract

Primates are very selective in the foods they include in their diets with foraging strategies that respond to spatial and temporal changes in resource availability, distribution and quality. Colombian woolly monkeys (Lagothrix lagotricha lugens), one of the largest primate species in the Americas, feed mainly on fruits, but they also eat a high percentage of arthropods. This differs from closely related Atelid species that supplement their diet with leaves. In an 11 month study, we investigated the foraging strategies of this endemic monkey and assessed how resource availability affects dietary selection. Using behavioural, phenological, arthropod sampling and metabarcoding methods, we recorded respectively foraging time, forest productivity, arthropod availability in the forest and arthropod consumption. Scat samples and capturing canopy substrates (i.e. moss, bromeliads, aerial insects) were used for assigning arthropod taxonomy. The most important resource in the diet was fruits (54%), followed by arthropods (28%). Resource availability predicted feeding time for arthropods but not for fruits. Further, there was a positive relationship between feeding time on fruits and arthropods, suggesting that eating both resources during the same periods might work as an optimal strategy to maximize nutrient intake. Woolly monkeys preferred and avoided some fruit and arthropod items available in their home range, choosing a wide variety of arthropods. Geometrid moths (Lepidoptera) were the most important and consistent insects eaten over time. We found no differences in the type of arthropods adults and juveniles ate, but adults invested more time foraging for this resource, especially in moss. Although woolly monkeys are generalist foragers, they do not select their food items randomly or opportunistically.

Figure 1

Arthropod consumption differences between adult and juvenile woolly monkeys (Lagothrix lagotricha lugens) at Cueva de los Guácharos National Park. Amplicon Sequence Variants (ASV’s) counts for each order of arthropod eaten by adult and juvenile woolly monkeys over the study period. Regardless of age class, woolly monkeys seem to eat in general the same types of arthropods and during the same periods of time. The heatmap indicates that the most eaten and selected arthropod for adults and juveniles are Lepidopterans. Light colours indicate low availability of ASV’s while darker colours indicate a high amount of ASV’s present in the woolly monkeys’ scats. Woolly monkeys artwork was painted by the biologist and artist Angela Mejía.

Figure 2

Fruit and arthropod preferences by Colombian highland woolly monkeys (Lagothrix lagotricha lugens) at Cueva de los Guácharos National Park. Results show the dietary preferences of fruits (green circles) and arthropods (orange triangles), y-axis shows how much an item is eaten compared to its availability, Jacobs’ selectivity index (D), and compared to x-axis how much each item is present in the monkeys diet (%). Items with higher values than 0.5 are the most selected, while below − 0.5 are among the most avoided by the monkeys.

Figure 3

Arthropod and fruit availability at Cueva de los Guácharos National Park. (a) Arthropod abundance (orange) over time. In general, availability is quite constant over time and peaks during the first months of the year, experiencing a decrease during the last months of the study. Light orange shadow around each point indicates the standard error. (b) Seasonal variation of fruits (green) over time, y-axis shows the mean month fruit productivity in terms of kg/ha. Productivity peaks twice a year during the months of March and September, light green shadow indicates the standard error.

Figure 4

Arthropod abundance and consumption comparison by Colombian highland woolly monkeys (Lagothrix lagotricha lugens) at Cueva de los Guácharos National Park. (a) Results of relative arthropod abundance show the changes of different orders of arthropods during the study. Changes in composition and abundance of arthropods at Cueva de los Guácharos National Park, shows how constant humidity can harbour arthropods all over the year. (b) Relative abundance of arthropods Amplicon Sequence Variants (ASV) present in the woolly monkeys’ scats. Results show a constant preference during the entire study for Lepidopterans (i.e. geometer moths) and few variations in the consumption of the most relevant arthropods during the study.