Nayuta Yamashita

Global patterns of leaf mechanical properties

Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plant-animal interactions and ecosystem functions across the globe.

Evolution and function of routine trichromatic vision in primates.

Abstract Evolution of the red-green visual subsystem in trichromatic primates has been linked to foraging advantages, namely the detection of either ripe fruits or young leaves amid mature foliage. We tested competing hypotheses globally for eight primate taxa: five with routine trichromatic vision, three without. Routinely trichromatic species ingested leaves that were “red shifted” compared to background foliage more frequently than species lacking this trait. Observed choices were not the reddest possible, suggesting a preference for optimal nutritive gain. There were no similar differences for fruits although red-greenness may sometimes be important in close-range fruit selection. These results suggest that routine trichromacy evolved in a context in which leaf consumption was critical.

Functional dental correlates of food properties in five Malagasy lemur species

Biomechanical explanations are fundamental to studies of functional dental morphology. Until recently foods were not classified in mechanical categories amenable to a rigorous examination of the fundamental physical relationship between teeth and foods. Fruit, insect and leaf categories, although descriptive, are mechanically heterogeneous. The diets of five Malagasy lemur taxa were described in terms of two mechanical properties, hardness and shear strength, in an earlier study (Yamashita, 1996b). In the present study, correlations between these two physical food properties and second molar tooth features of two lemur families are examined. Several relationships are hypothesized: 1) crest length is expected to be positively correlated with food shear strength; 2) the radius of curvature (r) of cusps is expected to be positively correlated with food hardness; and 3) basin area should increase relative to cusp radius as food hardness increases, and cusp-to-basin ratios should decrease with increasing food hardness. Two additional hypotheses address the debate concerning the relative influences of the most frequently eaten foods versus the most stressful foods in determining tooth form. The results of the predicted relationships are equivocal. 1) Crest length is negatively instead of positively correlated with strong foods. Crest lengths are correlated with quantities of leaf consumption, which are related to leaf shape more than to material composition. 2) As expected, r is positively correlated with food hardness and negatively with shear strength, but this applies to upper molar cusps only. Lower molar cusps complicate simple generalizations of relationships. 3) Hard foods are correlated with a tight fit of occluding cusps and basins instead of the expected loose fit. The most stressful foods eaten (hardest and strongest) have higher correlations with tooth features than the most frequently eaten foods. Several functional complexes can be identified. Hard food items are correlated with short cusps in lemurids, tight occlusal fit, small trigon and large talonid areas, and deep, acute basins. Large, shallow trigons, shallow, unrestricted talonids, and large upper molar basins are indicative of a diet of strong foods. These results demonstrate that some variation in tooth features is explicable with reference to mechanical properties of diet, although the relationships are complex.

Field kit to characterize physical, chemical and spatial aspects of potential primate foods

An outline is given for a field kit aiming to substantially increase the in situ knowledge gleaned from feeding studies of primates. Measurements are made of colouration (spectrum of non-specular reflection) and many mechanical, chemical and spatial properties of primate foods.

Diets of Two Lemur Species in Different Microhabitats in Beza Mahafaly Special Reserve, Madagascar

Studies of primate diets usually focus on differences that distinguish species or populations. However, variation in diet can occur at a more local level of groups within a population, especially in a non-homogeneous habitat. I compared dietary variation in food composition and toughness across groups of 2 lemur species in Beza Mahafaly special reserve, Madagascar. Beza Mahafaly contains an 80-ha reserve (Parcel 1) that, while small, hosts a dense population of Lemur catta (ring-tailed lemurs) and Propithecus verreauxi verreauxi (sifakas). Microhabitats in the eastern vs. western sides of the parcel are structurally and floristically distinct. Sifakas in this parcel have small, discrete home ranges and are morphological folivores. For these reasons, I expected that the 6 groups studied would eat a different menu of food plants but with similar toughness values. Ring-tailed lemurs have comparatively large, overlapping home ranges, and I expected that the 5 study groups would eat similar foods. Despite living in different microhabitats across the parcel, sifakas exhibit high dietary uniformity both in dietary plant species composition and the toughness of the foods. Food selection in sifakas operates on two distinct levels. Sifaka groups share many key food species that appear independent of local abundances, but the ranking of the foods within each group appears related to availability. Ring-tailed lemur groups are more heterogeneous in the composition of their diets relative to sifakas, though the time spent feeding on individual foods reveals a marked preference for the fruits of Tamarindus indica by all groups. Food toughness is consistent across the parcel with the exception of the most western group. Ring-tailed lemurs are highly specific feeders, but indiscriminate nibblers. Sifakas are targeted, balanced feeders. There does not appear to be a consistent microhabitat effect operating across species. Differences within sifaka and ring-tailed lemur populations in food composition and toughness, however, correspond to an east-west microhabitat gradient. Measures of dietary flexibility must take into account not only the plant species consumed and the different parts eaten but also their associated food properties and proportion of time spent feeding on them.

Seasonally and site specificity of mechanical dietary patterns in two malagasy lemur families (Lemuridae and Indriidae)

Relationships between tooth morphology and physical food properties are well established. Because food breakdown is initiated by the dentition, one may posit that variations in tooth form are related functionally to the physical demands placed on them by the diet. Yet classification of diets as leaves, fruits,and insects does not adequately describe foods in mechanically significant ways. Furthermore, physical dietary properties have not been well quantified. I describe patterns of two physical food properties — hardness and shear strength — in the diets of five lemur taxa in Madagascar— Propithecus diadema edwardsi, Lemur fulvus rufus, and Lemur rubriventer—in the rain forest site of Ranomafana National Park and Propithecus v. verreauxiand Lemur cattaat the dry forest site of Beza Mahafaly special reserve. I compared mean plant values for each lemur taxon, the most stressful foods eaten and the amount of time spent feeding on each dietary item. Variation in food hardness is a site phenomenon with fluctuations within sites. Shear strength is strongly seasonal. Lemur diets, as traditionally classified, are not mechanically uniform since frugivores and folivores could be separated on the basis of the physical properties of their foods. Finally, I assign taxa to dietary categories that are mechanically descriptive and derive several predictions regarding expected tooth morphologies from them.

Effect of Habitat Structure on Positional Behavior and Support Use in Three Species of Lemur

This study compares locomotor and postural behavior and substrate use of three species of lemur, the diademed sifaka (Propithecus diadema edwardsi), the brown lemur (Eulemur fulvus rufus), and the red-bellied lemur (Eulemur rubriventer) at two different localities within Ranomafana National Park. The object of the study is to see if there are quantitative differences in the behavior of the lemurs or their choice of substrates in forests that have different structural attributes. Analysis of the physical characteristics of the habitat demonstrates that compared to the Talatakely area, the forest at Vatoharanana has a higher proportion of larger, taller trees. The behavior of the lemurs also differs in the two areas: all species leap less and climb and move quadrupedally more at Vatoharanana. All species use small size supports less frequently at Vatoharanana, choosing insted medium size supports (all three species) or tiny supports (Propithecus andE. fulvus) found in tree crowns and terminal branches. The lemurs prefer (i.e. use more often than would be expected based on abundance) large trees at both sites. At Vatoharanana however, they are more frequently observed higher in trees and in taller trees with greater trunk breadth.The differences in locomotor behavior are in part due to the fact that at Vatoharanana, more bouts are collected during feeding and foraging than during travel. The relationship between this difference in activity pattern and the structural differerences in the two forests, however, is not clear. This study points out the need for longer term field studies of positional behavior and substrate use that incorporate the variety of forest types the subject species inhabit.

Light levels used during feeding by primate species with different color vision phenotypes

The intensity of available light is important in determining how well a diurnal animal can distinguish color. Primates with different types of color vision may exhibit behaviors that maximize visual contrast during critical activities such as feeding. We hypothesized that (1) trichromatic taxa will feed in a wide range of light conditions because color constancy permits stabilized color appearance across changes in illumination, and (2) that taxa with a high proportion of dichromatic individuals will tend to feed at higher light levels to increase color contrast. We recorded light levels during feeding bouts of seven primate taxa with varying degrees of color vision: the dichromatic Lemur catta, two polymorphic species, Propithecus v. verreauxi and Ateles geoffroyi, and the routine trichromats, Alouatta palliata, Colobus guereza, Piliocolobus badius, and Cercopithecus ascanius. Results were equivocal for our hypotheses. While routinely trichromatic taxa used varying light levels, the pattern of results did not differ from the dichromatic Lemur catta. However, polymorphic taxa not only sought the highest light, but females, which are the only individuals in polymorphic taxa that can be trichromatic, fed in higher light levels than males when eating non-green foods. This result is consistent with selection operating to maintain a balanced polymorphism in these taxa, though the connection between light levels and color vision type for the females is unclear. Our results further suggest that trichromatic vision may afford a selective advantage because it permits foraging under a greater range of light levels.

Linking Laboratory and Field Approaches in Studying the Evolutionary Physiology of Biting in Bamboo Lemurs

A realistic understanding of primate morphological adaptations requires a multidisciplinary approach including experimental studies of physiological performance and field studies documenting natural behaviors and reproductive success. For primate feeding, integrative efforts combining experimental and ecological approaches are rare. We discuss methods for collecting maximum bite forces in the field as part of an integrated ecomorphological research design. Specifically, we compare maximum biting ability in 3 sympatric bamboo lemurs (Hapalemur simus, H. aureus, and H. griseus) at Ranomafana National Park, Madagascar to determine if biting performance contributes to the observed partitioning of a shared bamboo diet. We assessed performance by recording maximum bite forces via jaw-muscle stimulations in anesthetized subjects from each species. Behavioral observations and food properties testing show that the largest species, Hapalemur simus, consumes the largest and most mechanically challenging foods. Our results suggest that Hapalemur simus can generate larger bite forces on average than those of the 2 smaller species. However, the overlap in maximum biting ability between Hapalemur simus and H. aureus indicates that biting performance cannot be the sole factor driving dietary segregation. Though maximum bite force does not fully explain dietary segregation, we hypothesize that size-related increases in both maximum bite force and jaw robusticity provide Hapalemur simus with an improved ability to process routinely its more obdurate diet. We demonstrate the feasibility of collecting physiological, ecological, and morphological data on the same free-ranging primates in their natural habitats. Integrating traditionally laboratory-based approaches with field studies broadens the range of potential primate species for physiological research and fosters improved tests of hypothesized feeding adaptations.

Food Physical Properties and Their Relationship to Morphology: The Curious Case of kily

17.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 17.2 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 17.2.1 Study Site and Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 17.2.2 Plant Collection and Mechanical Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 17.2.3 Tooth Morphometrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 17.2.4 Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 17.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 17.3.1 Kily Contribution to Lemur Diets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 17.3.2 Mechanical Properties of Kily Plant Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 17.3.3 Molar Morphometrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 17.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 17.4.1 Comparisons of Tooth Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 17.4.2 Comparisons with Larger Diet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 17.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404