On the other hand, leaf defenses used against insects are targeted to microscale
levels compared to those used against mammals [26]. For example, leaves of the
evergreen shrub Pseudowintera colorata are protected from herbivorous insects by
increased chemical defenses at leaf margins, which are usually red-pigmented [27].
Because many herbivores initiate feeding at the leaf edges, it is at least possible that
the marginal anthocyanins function as a visual signal to indicate that the leaves
contain unpalatable compounds [27]. Edge feeding is common among orthopteran,
coleopteran, and lepidopteran larvae [28] and damages leaves through increased
water loss and risk of infection [29]. Thus, defensive chemicals may be abundant at
leaf margins, where herbivorous insects prefer to initiate feeding [27]. In the
cottonwood Populus angustifolia, the total phenolic contents increase from the
base to the top of the leaf, which may affect the establishment site selection by the
stem mothers of the aphid Pemphigus betae [30]. Such a microscale distribution of
leaf defensive chemicals may also affect feeding behavior of herbivorous mammals.
Tree leaves are more abundant and common food resources of herbivores than
grasses, fruits, nuts, and seeds. However, the relationships between food selectivity
and plant chemicals are not fully understood in tree-leaf eating mammals as compared with those graminivores (herbaceous plant eaters), frugivores (fruit eaters),
and granivores (seed and nut eaters). Tree-leaf eating mammals are generally limited
to arboreal primates, rodents, and marsupials. Grand-dwelling mammals sometimes
use tree leaves as food resources. In this chapter, first, we review the effects of leaf
chemicals on tree-leaf eating mammals in the four hierarchical structures, between
tree species, conspecific trees, leaves in the same tree, and leaf parts. Second, we
show how leaf chemicals and herbivore’s feeding behavior change in the seasonal
environments. In the temperate mixed forest, all tree leaves are available for leafeating mammals in summer, but only evergreen trees are available in winter (Fig. 1).
The leaf chemicals also change with leaf ages. Finally, as a case study, we show the
relationships between leaf chemicals and feeding behavior of Japanese giant flying
squirrels Petaurista leucogenys. They have a peculiar leaf-feeding manner, eating a
central part of a single leaf. The measurements of the microscale distributions of
chemicals within the single leaf and the seasonal patterns of available trees differing
in leaf chemicals suggest that sugar concentration is an important factor affecting
which species of trees they eat, and total phenolic concentration affects which parts
of the single leaf they eat.
2
Effects of Tree-Leaf Chemicals on Feeding Behavior
2.1
Which Species of Leaves They Eat
Effects of chemical components of tree leaves on food selection have been reported
for several tree-leaf eating mammals such as primates, rodents, marsupials, and those
feeding tree leaves in some occasions. Various chemical components (e.g., energy,
sugar, carbohydrate, fibers, proteins, secondary metabolites, and other chemicals) are
tested for their food selection (Table 1).
15 Tree-Leaf Chemicals and Feeding Behavior of Arboreal Mammals in Seasonal. . .
347
levels compared to those used against mammals [26]. For example, leaves of the
evergreen shrub Pseudowintera colorata are protected from herbivorous insects by
increased chemical defenses at leaf margins, which are usually red-pigmented [27].
Because many herbivores initiate feeding at the leaf edges, it is at least possible that
the marginal anthocyanins function as a visual signal to indicate that the leaves
contain unpalatable compounds [27]. Edge feeding is common among orthopteran,
coleopteran, and lepidopteran larvae [28] and damages leaves through increased
water loss and risk of infection [29]. Thus, defensive chemicals may be abundant at
leaf margins, where herbivorous insects prefer to initiate feeding [27]. In the
cottonwood Populus angustifolia, the total phenolic contents increase from the
base to the top of the leaf, which may affect the establishment site selection by the
stem mothers of the aphid Pemphigus betae [30]. Such a microscale distribution of
leaf defensive chemicals may also affect feeding behavior of herbivorous mammals.
Tree leaves are more abundant and common food resources of herbivores than
grasses, fruits, nuts, and seeds. However, the relationships between food selectivity
and plant chemicals are not fully understood in tree-leaf eating mammals as compared with those graminivores (herbaceous plant eaters), frugivores (fruit eaters),
and granivores (seed and nut eaters). Tree-leaf eating mammals are generally limited
to arboreal primates, rodents, and marsupials. Grand-dwelling mammals sometimes
use tree leaves as food resources. In this chapter, first, we review the effects of leaf
chemicals on tree-leaf eating mammals in the four hierarchical structures, between
tree species, conspecific trees, leaves in the same tree, and leaf parts. Second, we
show how leaf chemicals and herbivore’s feeding behavior change in the seasonal
environments. In the temperate mixed forest, all tree leaves are available for leafeating mammals in summer, but only evergreen trees are available in winter (Fig. 1).
The leaf chemicals also change with leaf ages. Finally, as a case study, we show the
relationships between leaf chemicals and feeding behavior of Japanese giant flying
squirrels Petaurista leucogenys. They have a peculiar leaf-feeding manner, eating a
central part of a single leaf. The measurements of the microscale distributions of
chemicals within the single leaf and the seasonal patterns of available trees differing
in leaf chemicals suggest that sugar concentration is an important factor affecting
which species of trees they eat, and total phenolic concentration affects which parts
of the single leaf they eat.
2
Effects of Tree-Leaf Chemicals on Feeding Behavior
2.1
Which Species of Leaves They Eat
Effects of chemical components of tree leaves on food selection have been reported
for several tree-leaf eating mammals such as primates, rodents, marsupials, and those
feeding tree leaves in some occasions. Various chemical components (e.g., energy,
sugar, carbohydrate, fibers, proteins, secondary metabolites, and other chemicals) are
tested for their food selection (Table 1).
15 Tree-Leaf Chemicals and Feeding Behavior of Arboreal Mammals in Seasonal. . .
347