Mitchell T. Irwin

Objectives: Primatologists have documented diversity in diet types (frugivore, folivore, etc.) and nutritional differences among those foods, but little is known about intakes (incorporating food compositions and intake amounts). Therefore, how nutritional outcomes and constraints differ across diet types remains poorly understood. We documented diet and nutrient intakes in sympatric lemurs across > 1 year at Tsinjoarivo‐Ambalaomby, Madagascar: Propithecus diadema (folivore) and Eulemur fulvus (frugivore). Materials and Methods: We combined focal animal feeding data with lab analyses to generate daily intakes of food, energy, and nutrients, testing for species and seasonal differences using linear mixed models, and visualizing data using nutritional geometry. Results: E. fulvus consumed 2.7 times more food than P. diadema , accomplished largely through fast intake. E. fulvus had higher energy and nutrient intake; this included three times more protein and higher proportional contribution of protein, despite lower protein in fruit (accomplished by eating more, and supplementing with high‐protein leaves). Lean season response diverged: E. fulvus increased feeding and had similar non‐protein energy but higher protein intakes, while P. diadema decreased effort and tolerated reduced protein and non‐protein energy intakes. Discussion: General fruit‐leaf nutritional differences do not drive nutrient intakes; instead, the “efficiency‐velocity continuum” (frugivores eating more and digesting less fully) is key to understanding frugivore and folivore ecology, including nutrient intakes, food selection rules, and factors limiting abundance. Primate frugivores may not be as protein‐limited as previously assumed. However, future research must examine how absorption rates (across species, habitats, and seasons) affect actual nutrient intakes and energy/nutrient balance.

Collecting observational data on nocturnal lemurs in the wild is challenging, resulting in limited information on their natural history, ecology, and evolution. Avahi laniger and Lepilemur mustelinus are two small, nocturnal lemurs that appear to defy the rules of folivory (being almost exclusively folivorous despite small body size) and are highly understudied. This research aimed to describe the nutritional ecology of these lemurs to better understand their adaptations to a folivorous diet. We collected eight weeks of behavioural data, including feeding behaviour, in October-December 2020 in Tsinjoarivo, Madagascar. Additionally, we collected thirty-three plant foods, which we observed the two species consuming, for nutritional analyses. Both species were mostly observed resting, a common behavioural adaptation for processing a folivorous diet, but differed in periods of peak feeding behaviour. A. laniger and L. mustelinus had very little dietary overlap: only five of 34 total plant species were consumed by both species and one of these shared foods was the same species, but different parts. The nutritional composition of A. laniger and L. mustelinus ’ foods were largely similar, but diverged in one nutritional variable: L. mustelinus consumed foods higher in available protein than A. laniger . Both species also approached plant secondary metabolites differently: A. laniger tolerated tannins while as L. mustelinus tended to avoid them. This research, the first nutritional ecology study of Avahi laniger and Lepilemur mustelinus in Tsinjoarivo, is consistent with previous suggestions of niche separation through food chemistry.

Many primate species consume insects as part of their regular diet, yet few researchers have systematically collected them and analyzed their nutritional content. In this study, we developed protocols for collecting and analyzing prey items consumed by Weddell’s saddleback tamarins ( Leontocebus weddelli ), focusing on Orthoptera (crickets, grasshoppers, and katydids) which have been documented to be a central component of their diet. We used five methods to collect insect prey (pitfall, sheet, water, moth trap and manual capture) at a field site in northwestern Bolivia over the course of two months. In total, we collected 1302 insect samples, which we photographed, weighed, dried, and sorted into nine taxonomic groups (Acrididoidea/Eumastacoidea, Blattodea, Cicadoidea, Gryllidae, Lepidoptera, Mantodea, Phasmatodea Proscopiidae, and Tettigoniidae). We then analyzed the samples for their macro- and micro-nutrients. We found that the manual capture method was the most effective for capturing orthopterans. Our analyses showed that the samples primarily contained crude protein (52.63-78.54 % dry matter (PCDM)), chitin (12.05-27.26 PCDM) and fat (4.63-15.6 PCDM). The samples also contained high levels of a wide variety of minerals, including iron (42-655 parts per million (ppm)), zinc (85-554 ppm), and manganese (37-1200 ppm). These results indicate that orthopterans and other Neotropical insects can serve as important sources of macro- and micronutrients for tamarins. Given the variation in nutrient content among taxa, we recommend that researchers collect and analyze insects that most closely resemble the prey consumed by their study subjects to determine their nutritional value, and not assume equivalent nutritional composition across species, higher taxa, or life stages. Given the success of using night walks with manual capture for collecting Orthopterans, we recommend that other primatologists use this method to allow for cross-site comparisons of insect nutrition.

Our study aimed to (1) determine how the shape varies and mechanisms influence species‐area relationships within the same taxon but between different ecoregions and (2) determine how slope ( z ) and intercept ( c ) values of the linearized power model were influenced by ecoregion. Location: Madagascar. Taxon: Arboreal mammals (lemurs). We surveyed arboreal mammals (lemurs) in 42 tropical dry deciduous forest fragments in Ambanjabe Field Site in Ankarafantsika National Park in Western Madagascar and 27 primary mid‐elevation raiforest fragments in the Tsinjoarivo‐Ambalaomby new protected area in Eastern Madagascar using line‐transect methods. We determined which of 20 species‐area models were the most likely using the ‘ sars ’ R package and AICc in each ecoregion. We compared z and c values of the power model in each ecoregion using ANCOVA. We assessed what drove the shape of the SARs using the Measurement of Biodiversity framework. We found that SAR models differed between ecoregions, with the power model (AICc = 89.04) as the most likely in the west and the Monod model (AICc = 86.98) followed by three candidate models (Kobayashi, AICc = 87.02; logarithmic, AICc = 87.6; and negative exponential, AICc = 88.61) in the east. We found no significant difference in z values between ecoregions ( F _1,66 = 2.991, p = 0.088) and a non‐significant trend in c values between ecoregions ( F _1,65 = 3.938, p = 0.051). Spatial aggregation of species drove species richness patterns in the west, and species diversity and evenness drove species richness patterns in the east. Our study demonstrates that while the power and negative exponential model are good starting points, other models are also likely models to describe SARs in arboreal mammals such as primates. These patterns can reflect different mechanisms driving SARs. Ecoregion was not strongly related to differences in either z or c values of the power model.

Frugivorous primates may consume unusual food items, such as plant galls, to meet their nutritional requirements; yet, the contributions of these dietary components to their diet, nutrition requirements, and energy intakes are still unclear. We documented the importance of plant galls in these aspects for black‐and‐white ruffed lemurs (Varecia variegata) in a Malagasy rainforest. Using daily observation data of lemur foraging and nutritional analyses of their consumed items, we measured (1) the proportion of galls in their diet, (2) the rate at which they acquire nutrients and energy from galls compared to other food items, and (3) the changes in their diet patterns and acquisition of nutrients and energy with the consumption of galls. We also investigated whether they are more likely to consume fruits on trees with galls and characterized whether galls have similar characteristics as fruits. We found that plant galls constituted 12.96% of the lemur feeding occurrences; and on some days, lemur diets comprised galls only. Also, the lemurs acquired from galls higher protein than any other food items and higher sugar, fiber, and energy than leaves, but lower lipid than fruits and similar nutrients and energy as from flowers. The addition of galls in their diet significantly reduced their consumption of ripe fruits on a daily basis and increased the acquisition of protein, sugar, fiber, and energy. Also, lemurs were more likely to consume fruits on trees with galls than expected, likely due to similarities in color and nutrient components between galls and fruits in this system. These findings enhance our understanding of the nutritional needs and food selection behavior of primate frugivores. Such knowledge has implications for developing strategies to maintain primate populations in their natural environments and potentially to ensure the welfare of captive animals in ex‐situ conservation settings.

Despite traditional dietary categories common in primatology (folivore, frugivore, insectivore), most primates use one or more food types beyond their primary one. Among lemurs, folivores tend to have a complicated, long gastrointestinal tract with an enlarged cecum, shearing teeth, and microbiome adaptations to foliage, while frugivores have simple teeth and guts and fast gut passage. Yet frugivores often eat some leaves, and folivores eat some fruit, and little is known about the selection rules they follow within each food type. We quantified diet and food chemistry for two sympatric rainforest lemurs: a cathemeral frugivore (brown lemur, Eulemur fulvus) and a diurnal folivore (diademed sifaka, Propithecus diadema) over 18 and 13 months. Brown lemurs ate 78.3% fruit and 13.0% leaves; sifakas ate 52.8% leaves and 37.9% fruit/seed; both ate fruit/seed most in the resource‐abundant season, increasing leaf/flower consumption in the lean season. Both had diverse diets (128 and 81 plant species) but selected almost entirely different species; however, within fruit and leaf categories, their foods overlapped substantially in nutritional content. They were more selective in their secondary foods: sifakas selected higher‐energy fruits and brown lemurs selected leaves higher in protein and minerals. This indicates a balancing function: frugivores selecting leaves strategically to compensate for low‐protein, low‐mineral fruit and folivores selecting fruit/seed to compensate for low‐energy leaves. That said, it is puzzling why sifakas ignored some leaf species eaten by brown lemurs that were high in protein and minerals—this suggests these nutrients are not prioritized or limiting for sifakas. Other factors likely contribute to the mutual exclusivity in food selection, particularly plant secondary metabolites not measured here or the (poorly‐understood) metabolic costs of eating nutrients in excess. More research is needed to fully understand food choices, how these promote niche differentiation, and their consequences for animals, communities, and ecosystems.

The concept of “facilitated restoration” aims at native biodiversity reinstatement with the help of animal seed dispersers attracted by fruiting trees. Yet, large-crowned trees will have to develop in the early stages of restoration; therefore, seed dispersal provided by small generalist mammals and birds that use rapidly growing herbs, shrubs, and small trees at early stages of forest succession would accelerate biodiversity restoration. Due to the elusive lifestyle of these small animals, it is unclear what species can contribute to the early stages of this process. Using the primate genus Microcebus (adult body mass about 60 g) as an example, we illustrate that these small generalists are possible seed dispersers in the early stages of forest restoration, not yet used by larger frugivores. We show that Microcebus spp. dispersed more seeds from herbs, shrubs, and small trees than large frugivorous primate species. These plants tend to have smaller seeds than large tree species and are often pioneer species not considered in forest restoration projects. Facilitating the colonization of restoration plots by generalist small seed dispersers that use shrubby habitats may improve plant diversity by adding a more natural sequence of successional stages towards mature forests in Madagascar and elsewhere in the tropics.

Conservation funding is currently limited; cost‐effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID‐19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km ² than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly.