Introduction:
The dwarf mongoose and hornbill bird share an interesting
mutualistic relationship for several reasons. Their spectra of prey and
predators are nearly identical (4), making this relationship even more
important for both parties involved. In this partnership the hornbill bird eats
the leftover insects during the foraging process of the dwarf mongoose (3). In
exchange for food, the hornbill warns the dwarf mongoose if a predator is
approaching. Both dwarf mongooses and hornbill birds are distributed in much of
southeast Africa (2). In regard to their lifecycles, dwarf mongooses reach
sexual maturity at one year of age and usually produce an average of five pups
per litter (2). Hornbill birds usually form monogamous relationships and
usually lay six eggs per birthing cycle (5). Additionally, dwarf mongooses
generally sleep in old termite mounds, and hornbill birds can usually be found
in the trees above these termite mounds awaiting for the dwarf mongooses to
wake up and start foraging for food (4).
Description of the Relationship:
Helogale
parvula (dwarf mongoose) and Bucerotidae (hornbill bird) have such a close relationship that they almost seem to
seek each other out in their daily lives (4). In the morning, hornbills wait
for the mongooses to awaken and when the mongooses start foraging for food the
hornbills happily eat the leftover insects (3). Since the mongooses are
foraging for food it is up to the hornbills to warn the mongooses of
approaching predators like a black eagle. Anne E. Rasa
states in her paper that, “This is the closest known mutualistic relationship
known between social vertebrates normally living independently (4).” Therefore,
in regard to the evolutionary history of the relationship, it can be assumed
that this partnership has increased the evolutionary fitness of both parties
involved. The relationship is established by the mongoose providing food for
the hornbill and the hornbill providing protection for the mongoose (5). Our
text explains mutualism as “opposed to parasitic systems, in a mutualistic
system each partner takes advantage of the association between the two
protagonists (1) (Claude Combes, 553).” It is clear that the mongoose and
hornbill fully exemplify this definition of mutualism.
Cost/Benefit Analysis:
When conducting a cost/benefit analysis in mutualism it is
important to bear in mind that, in most cases, the benefits outweigh the cost.
The cost for the dwarf mongoose in this relationship is decreasing the total
amount of food it is able to intake because the hornbill birds are eating from their
same food supply (2). The benefit for the mongoose is protection from predators
when the hornbills willingly signal a warning call. The cost for the hornbills
is using valuable energy to signal a warning call for the mongooses to be
warned of approaching predators (3). However, the benefit for the hornbills is
the ease of finding excess food, in the form of easily accessible leftovers,
when the mongooses are out foraging. The benefit of the hornbills outweighs the
cost in that simply finding food is more valuable than the lost energy in
providing the mongooses with a warning call. The benefit of the mongoose
outweighs the cost in that it is better to have a slightly decreased food
supply compared to being killed by a predator. Moreover, a specific strategy
employed by the hornbills to ensure participation of the mongooses is living in
trees close to termite mounds and waiting for the mongooses to wake up to begin
foraging for food (4). Overall, the mutualistic relationship between the dwarf
mongoose and the hornbill bird is one that contains a relatively low cost and
reaps a relatively high reward.
References:
(1) Combes, Claude. Parasitism:
The Ecology and Evolution of Intimate Interactions; Translated by Isaure De
Buron and Vincent A. Connors ; with a New Foreword by Daniel Simberloff.
Chicago: University of Chicago, 2001. Print.
(2) "Dwarf Mongoose." African
Wildlife Foundation. Web. 17 Mar. 2012.
<http://www.awf.org/content/wildlife/detail/dwarfmongoose>.
(3) "Hornbill Family
Bucerotidae." Don Roberson Creagrus. Web. 17 Mar. 2012.
<http://creagrus.home.montereybay.com/hornbills.html>.
(4) Rasa, Anne E. "Dwarf
Mongoose and Hornbill Mutualism in the Taru Desert, Kenya." Behavioral
Ecology and Sociobiology 12.3 (1983): 181-90. Print.
(5) "Red-billed Hornbill."
World Association of Zoos and Aquariums (WAZA). Web. 17 Mar. 2012. <http://www.waza.org/en/zoo/pick-a-picture/tockus-erythrorhynchus>.
I would like to use the image of the hornbill with dwarf mongooses in a book that I am writing. Please contact me to discuss this. Lynn Hurry Cape Town lynn@ecology.co.za
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