| MadSci Network: Botany |
Botany textbooks rarely give examples of plant-animal commensalisms because animals usually either benefit or harm plants. Perhaps the closest to a plant- animal commensalism is an animal living or nesting in a tree as birds and squirrels do. However, animal droppings might provide mineral nutrients for the tree, and some birds eat insects that attack trees. Squirrels often disperse tree seeds that benefits a tree. Many textbooks state that epiphytes, plants that live on other plants, represent a plant-plant commensalism. However, epiphytes are considered to be "nutritional pirates" because they intercept a lot of mineral nutrients that would otherwise go to the host tree. Large numbers of epiphytes in a tree can cause branch breakage because of their weight. Large numbers of epiphytes may also shade out portions of the host tree. The strangler figs (Ficus species) start out as epiphytes but then send roots to the ground, wrap the roots around the host trunk and eventually kill the host tree. Plant-animal mutualisms are much more common than plant-animal commensalisms, including animals as pollinators, animals as seed dispersers and ants that protect some Acacia tree species from enemies in return for a home and food. Some plants "cheat" their pollinators by not providing the usual nectar rewards. The bee orchids (Ophrys species) have flowers that resemble female bees. They trick the male bees into mating with the flower and pollinating them. It is a matter of opinion whether the male bees benefit and it is a mutualism, the male bees are harmed and it is a parasitism, or the male bees receive no benefit or harm and it is a commensalism. You might say cocklebur and other plants with fruits or seeds with barbs that stick to animals and hitch a ride represent a commensalism. The animal is probably not harmed but receives no benefit from transferring the fruit/seeds. References Bee orchids Re: How do burrs stick to clothing Ant-Acacia Mutualism Ant-Acacia Mutualism Strangler Fig
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