Flowering plants, being sedentary, have co-opted animal partners for purposes of gene exchange and propagule dispersal, through pollination and seed dispersal. To secure these services plants provide a variety of flower or fruit rewards creating some of the most common and obvious mutualistic interactions in the natural world. However, plants are also eaten by animals which graze on leaves, bore through stems, or predate seeds. Plants have therefore evolved mechanisms to promote the efficiency of mutualistic interactions and protect against herbivores and seed predators. This article describes the range of ecologically significant plantanimal interactions that commonly occur in temperate and tropical forest systems. Most ?owering plants are animal pollinated, and indeed the function of ?owers is to attract animal vectors for pollen dispersal. Most ?owers offer a reward to pollinators which are usually nectar or pollen, but can also include resins (e.g. Clusiaceae), waxes, or oils (orchids). Pollinators attracted to ?owers collect the resources and in the process pick up pollen through contact with the anthers and deposit pollen they are carrying onto the stigma where pollen germinates and ultimately fertilizes the ovules.
[...] The most important herbivores in tropical forest habitats in terms of the amount of plant biomass consumed are insects, in both adult and larval forms. Grasshoppers, katydids, some beetles and ants, and the larvae of moths, butterﬂies, and many ﬂies and sawﬂies consume vast quantities of leaf material. Many other insect grazers, such as springtails, feed on root tissues. A large number of insects belonging to the orders Coleoptera (beetles), Lepidoptera (moths), Diptera (ﬂies), and Hymenoptera (sawﬂies) consume tissue between the epidermal layers of leaves creating conspicuous mines or blotches. [...]
[...] Plants have, in turn, evolved a wide array of defensive compounds or physical structures that impede insect or vertebrate attack. Chemical defenses can reduce the digestibility of leaf tissue, or may have a toxic or repellent function. Tannins are large carbon-rich compounds that bind proteins making them difﬁcult to digest. Toxic compounds include phenolics and alkaloids and these may poison or kill animals that consume them. Some plants have responded to attack by leaf miners by secreting latex which impedes or kills larvae. [...]
[...] In the tropical dry forest of Mudumalai Wildlife Sanctuary, southern India, very high tree mortality, largely a result of elephant damage, has been documented. Elephants are also known to play an important role in determining the abundance of trees in African savanna forests. In North America dam building by beavers can dramatically alter forest riparian habitats and, because they feed preferentially on deciduous species beavers cause an increase in the relative proportion of conifers. Animals that cause long-term and dramatic physical modiﬁcation of habitats have been termed ecosystem engineers and may be important for maintaining high species and structural diversity by increasing habitat heterogeneity. [...]
[...] The mutualism is also geographically widespread and has evolved independently at least twice among Acacia trees in Central American dry forests and African savanna forests, and the ferocity of weaver ants (Oecophylla) which construct nests from freshly woven leaves of a variety of trees is familiar to forest workers throughout Southeast Asia. In some cases (as for the plants Hydnophytum formicarium and Myrmecodia tuberosa) ants provide food for the plants by depositing their refuse in absorptive chambers that house the ants. [...]
[...] Honeybees pollinate many forest trees in tropical regions including many large canopy species, but solitary or semisocial species are also widespread pollinators occurring in forest canopy and understory. Although honeybees are very effective pollinators they are generalist in their foraging behavior and forage preferentially on species occurring at highest frequency or density. Such frequency-dependent foraging behavior does not, therefore, favor rare or highly dispersed plants which become more dependent on pollinators that may be more specialists in their ﬂoral resource requirements. [...]
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