Zoology

How Animals have Developed Symbiotic Relationships with their Environments over



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A symbiotic relationship is a convenience arrangement based on physical need. The natural environment is a world of inter-webbed ecosystems, laced with symbiotic relationships. Animals are a vital ingredient keeping ecosystems in "healthy" balance. To achieve this over time, many animals develop symbiotic, co-operative, interdependent relationships with other animal species and/or plants. The benefits usually involve food and protection; they may be mutual or one-sided.

At the highest, most observable level is the symbiotic relationship between animals and man. The evolution of this relationship has become more complex over time. Man generally provides more and more domesticated animals with protection and a reliable food source, while domesticated animals may provide food (eggs, milk and butter) or spiritual comfort for man. Man has been instrumental in creating new breeds. In the future, will this practice strengthen the animal and man connection? As this relationship evolves, there is often a secondary benefit of taming wild instincts, creating a level of mutual respect and understanding between animal and man. But, in time, will animals be the demanding master? Some cat owners may believe that is already the case.

Two cases of man and animal co-operation need a special mention. Isack and Reyer (1989) recorded that the honeyguide, a species of bird, leads the Borans of Kenya to honeybee colonies hidden in hollow trees. The Borans benefit because, with the help of the honeyguides, finding a hive takes 3.2 hours but 9 hours without help. The birds benefit from human help because they cannot access the desirable bee larvae and wax themselves. www.psypress.com And dogs and pigs are specially trained to seek out underground truffles, a form of fungi, but an extremely expensive gourmet food prized in Europe.

Symbiotic relationships in the desert areas still require extensive research. Most studies focus on the impact of rain on life in desert areas. But there is one fascinating case, separate from the influence of rain variables. Why do Australia's most arid areas have the most extensive ant life in the world? It is well-known that ants often protect sap-sucking insects. Insects can produce honey-dew, perhaps more common in Australia than elsewhere. Ants love honey-dew! Voila! A highly-productive, symbiotic relationship with mutual advantages! ("NT Country Hour" www.abc.net.au) So, over time, while there is sap, insects will feed, produce honey dew and the desert ant population can only keep on increasing!

Underwater research studies give evidence of a range of symbiotic relationships. Divers in the tropical waters around Papua New Guinea have revealed some fascinating examples. Some Goby species, for protection, live in the spines of toxic sea urchins. How did this evolve when the sea urchins seem to gain little? Gobies and shrimps act as cleaner fish. Shrimps even hitch a ride on sea cucumbers in return for the cleaning service. The client fish may change colour to signal "cleaning time" or to highlight the existence of parasites. Gobies and the partially blind shrimp species may co-habitate. The Goby guards the shrimp burrow till it is safe for the shrimp to emerge and the Goby gets a burrow to call home. Finally, there are the symbiotic "mimics". In self-defence, the Harlequin snake eel mimics the poisonous black and white Banded sea snake. And an octopus changes shape to enhance its predator skills and for protection. (www.ms-starship.com)

Coral reefs have afforded extensive study on a world scale. It is generally acknowledged that algae cells, attached to the coral polyps, (often denser in parts that are shaded), provide the means of processing the sun's energy, so that the coral can grow like a plant during the day. Further, the algae absorbs ultra-violet light, protecting the coral. At night, the coral acts like an animal, feeding on plankton captured with their tentacles. In return, the coral supplies nitrates and phosphates, vital for algae growth. (www.reef.edu.au and www.environment.newscientist.com) However, many reefs are under threat; in particular, the Great Barrier Reef off north-east Australia's coastline. Whether it be global warming, the rampant feeding habits of predator star fish or changing tides, coral is changing from colour magic to pasty white and dying in the process. Perhaps, in the near future, this symbiotic relationship will be no more.

In the rainforests, it seems symbiotic relationships are the rule rather than the exception. Is this because rainforests are becoming a fragile corner of our world? Do animals feel the pressure from human activities? To cite a couple of examples, in the Amazon rainforest, the brazil nut tree needs a ground rodent, known as an agouti, for its ongoing existence. The sharp teeth of the agouti breaks the seed pods, eats some seeds and scatters the rest in secret staches far from the parent tree. The buried seeds germinate; more brazil nut trees. Then there is the case of the caterpillar and the ant. "Certain caterpillar species produce sweet chemicals from "dew patches" on their backs, upon which a certain ant species will feed. In return, the ants vigorously protect the caterpillar and have even been observed carrying the caterpillar to the nest at night for safety." www.rainforests.mongabay.com

The more we discover animals' symbiotic relationships with their environment, the more we realize how environmental changes or threats impact on complex ecosystems. Symbiosis has triggered shifts in the natural evolution of a species. Would the honeyguides still exist without the help of man? And evolution continually spawns new symbiotic relationships. "Plovers pick leeches from crocodiles' teeth, offering dental hygiene in return for food." (www.environment.newscientist.com) No wonder the crocodile keeps smiling!

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