5
Conclusions
Tree leaves are much more abundant than other food resources of herbivores such as
seeds, nuts, and fruits, but arboreal mammals do not eat tree leaves randomly. Leaf
chemicals affect food choice and feeding behavior of them. They usually prefer
sugar- and protein-rich leaves but avoid those including more fibers and secondary
metabolites. Preference of sweeter leaves may be caused by its higher energy
contents and by which they acquire sufficient amount of food within a short time.
Protein (or N) is always limited for herbivores. Selective feeding of protein-rich
leaves may be adaptive for their long lives, but the physiological mechanism how
they select those leaves remains unknown. Fibers are generally avoided because of
decreasing digestibility and increasing toughness of leaves. Secondary metabolites
function in toxins (e.g., phenolics and alkaloids) and in digestion inhibitors (e.g.,
condensed tannins) and are usually avoided by their bitter taste or aversive postingestive feedback.
The effects of leaf chemicals on food choice of arboreal herbivores have been
examined in four comparative categories; between tree species, between trees of the
same species, between leaves of the single tree, and between the parts of a leaf. Most
studies revealed that arboreal herbivores prefer leaves of particular tree species or
young leaves. However, little information is available on selection between conspecific trees and partial eating of a leaf. Microscale distributions of chemicals may be
an important factor to know which parts of a leaf they eat. When preferable or
unpreferable chemicals are biased within the single leaf, they may eat partially.
Chemical-mediated partial eating of a leaf is one of the future studies to be solved.
On the other hand, leaf chemicals are not always constant but change seasonally. In
the temperate zone or dry and wet periods, tree physiology and leaf chemicals
change seasonally. In winter or dry seasons, leaves of deciduous trees are
unavailable and arboreal mammals select leaves only within evergreen trees. In
summer, however, they are surrounded by both types of trees in which a variety of
leaves are available not only in tree species but also in leaf chemicals. Seasonal
changes are repeated during individual lives, which enables them to learn appropriate feeding sites, leaf selection, and feeding manners based on temporally and
spatially changing leaf chemicals.
Acknowledgments We wish to thank Noriko Tamura, Mayumi Shigeta, Nickie Seto, and Brianna
Rico for assisting the field and some laboratory works. This study was partly supported by
competitive research funding from the Graduate School of Science and Engineering, Tokyo
Metropolitan University to FH in 2015 and by a Sasakawa Scientific Research Grant from the
Japan Science Society to MI in 2016. MI was also supported by a Research Fellowship for Young
Scientists of the Japan Society for the Promotion of Science in 2017–2019.
References
1. Glander KE (1982) The impact of plant secondary compounds on primate feeding behavior.
Am J Phys Anthr 25:1–18
370
M. Ito and F. Hayashi
Conclusions
Tree leaves are much more abundant than other food resources of herbivores such as
seeds, nuts, and fruits, but arboreal mammals do not eat tree leaves randomly. Leaf
chemicals affect food choice and feeding behavior of them. They usually prefer
sugar- and protein-rich leaves but avoid those including more fibers and secondary
metabolites. Preference of sweeter leaves may be caused by its higher energy
contents and by which they acquire sufficient amount of food within a short time.
Protein (or N) is always limited for herbivores. Selective feeding of protein-rich
leaves may be adaptive for their long lives, but the physiological mechanism how
they select those leaves remains unknown. Fibers are generally avoided because of
decreasing digestibility and increasing toughness of leaves. Secondary metabolites
function in toxins (e.g., phenolics and alkaloids) and in digestion inhibitors (e.g.,
condensed tannins) and are usually avoided by their bitter taste or aversive postingestive feedback.
The effects of leaf chemicals on food choice of arboreal herbivores have been
examined in four comparative categories; between tree species, between trees of the
same species, between leaves of the single tree, and between the parts of a leaf. Most
studies revealed that arboreal herbivores prefer leaves of particular tree species or
young leaves. However, little information is available on selection between conspecific trees and partial eating of a leaf. Microscale distributions of chemicals may be
an important factor to know which parts of a leaf they eat. When preferable or
unpreferable chemicals are biased within the single leaf, they may eat partially.
Chemical-mediated partial eating of a leaf is one of the future studies to be solved.
On the other hand, leaf chemicals are not always constant but change seasonally. In
the temperate zone or dry and wet periods, tree physiology and leaf chemicals
change seasonally. In winter or dry seasons, leaves of deciduous trees are
unavailable and arboreal mammals select leaves only within evergreen trees. In
summer, however, they are surrounded by both types of trees in which a variety of
leaves are available not only in tree species but also in leaf chemicals. Seasonal
changes are repeated during individual lives, which enables them to learn appropriate feeding sites, leaf selection, and feeding manners based on temporally and
spatially changing leaf chemicals.
Acknowledgments We wish to thank Noriko Tamura, Mayumi Shigeta, Nickie Seto, and Brianna
Rico for assisting the field and some laboratory works. This study was partly supported by
competitive research funding from the Graduate School of Science and Engineering, Tokyo
Metropolitan University to FH in 2015 and by a Sasakawa Scientific Research Grant from the
Japan Science Society to MI in 2016. MI was also supported by a Research Fellowship for Young
Scientists of the Japan Society for the Promotion of Science in 2017–2019.
References
1. Glander KE (1982) The impact of plant secondary compounds on primate feeding behavior.
Am J Phys Anthr 25:1–18
370
M. Ito and F. Hayashi