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The pro­gres­sive dis­ap­pear­ance of seed-​dispersing ani­mals like ele­phants and rhi­noc­er­oses puts the struc­tural integrity and bio­di­ver­sity of the trop­i­cal for­est of South-​East Asia at risk.

With the help of Span­ish researchers, an inter­na­tional team of experts has con­firmed that not even her­bi­vores like tapirs can replace them. The results of their study have been pub­lished in the Biotrop­ica journal.

“Mega­her­bi­vores act as the ‘gar­den­ers’ of humid trop­i­cal forests: They are vital to for­est regen­er­a­tion and main­tain its struc­ture and bio­di­ver­sity”, as was explained to SINC by Ahimsa Campos-​Arceiz, the lead author of the study and researcher at the School of Geog­ra­phy of the Uni­ver­sity of Not­ting­ham in Malaysia. In these forests in East Asia, the large diver­sity of plant species means that there is not enough space for all the trees to ger­mi­nate and grow. As well as the scarce light, seed dis­per­sion is made more com­pli­cated by the lack of wind due to the trees that are up to 90 metres high. Plant life is then lim­ited to seeds dis­persed by those ani­mals that eat pulp. They either scat­ter seeds by drop­ping their food, regur­gi­tat­ing it or by defe­cat­ing later on.

In the case of large seeds, “plants need a large ani­mal capa­ble of eat­ing, trans­port­ing and defe­cat­ing the seeds in good con­di­tions,” accord­ing Luis San­ta­maría, co-​author and researcher at the Mediter­ranean Insti­tute for Advanced Stud­ies (IMEDEA) of Spain’s CSIC Sci­en­tific Research Agency. This is where ele­phants and rhi­noc­er­oses come into play because they can scat­ter large quan­ti­ties of seeds thanks to the fact that they slowly digest very lit­tle of their food. How­ever, habi­tat loss, poach­ing, and the con­flict between ele­phant and man has caused a 95% loss in Asian ele­phant (Ele­phas max­imus) his­tor­i­cal dis­tri­b­u­tion range and has left the rhi­noc­eros just a step away from extinc­tion: there are less than 50 Java rhi­noc­er­oses (Rhi­noc­eros sondaicus) and 200 Suma­tra rhi­noc­er­oses (Dicerorhi­nus suma­tren­sis).

Accord­ing to the IUCN Red List of Threat­ened Species, ele­phants are in ‘dan­ger of extinc­tion’ and both the rhi­noc­eros species are ‘crit­i­cally endangered’.

Asian tapirs are no elephants

In light of the sit­u­a­tion, the research team eval­u­ated the seed-​dispersing capac­ity of another large her­bi­vore weigh­ing 300 kg. For cul­tural rea­sons it is not hunted and has a sim­i­lar diges­tive sys­tem to that of ele­phants and rhi­noc­er­oses: the Asian tapir (Tapirus indi­cus).

The study allowed researchers to ana­lyze the effect of dis­per­sion by tapirs on the seed sur­vival of nine dif­fer­ent plants. This included some large plant species such as the mango tree and durian, as well as other smaller species like the ‘ele­phant apple’ (Dil­lenia indica). Among other out­comes, the results show that tapirs defe­cated 8% of the tamarind seeds ingested (none of which ger­mi­nated) com­pared to ele­phants, who defe­cated 75% of the 2,390 ingested seeds (65% of which germinated).

Stop­ping ille­gal hunt­ing is the priority

“If these mega­her­bi­vores dis­ap­pear from the ecosys­tem, their con­tri­bu­tion to eco­log­i­cal processes will too be lost and the path of the ecosys­tem will change irre­versibly,” explains the lead author, who goes on to state that “the most prob­a­ble con­se­quences are the change in the struc­ture of the under­growth and the for­est and the loss of cer­tain species.” Ele­phants and rhi­noc­er­oses play a unique eco­log­i­cal role that can­not be replaced by other species. With­out large her­bi­vores, new large seed plants will always grow in close prox­im­ity to the mother plant and are there­fore “unable to colonise avail­able space in other for­est areas,” warns the IMEDEA researcher.

In this respect, those plant species that depend on large ani­mals will become increas­ingly rare whereas those that depend on the wind and smaller, abun­dant ani­mals will increase in terms of den­sity and dominance.

To avoid such a sce­nario, researchers sug­gest that megafauna should be pro­tected and in some cases mega­her­bi­vores should be rein­tro­duced into areas from where they had pre­vi­ously dis­ap­peared. “In the south-​east of Asia, the pri­or­ity is to stop ille­gal hunt­ing and mit­i­gate the impact of habi­tat loss,” indi­cates the expert, crit­i­cis­ing the “absurd” moti­va­tion to kill in order to sell their horns and tusks for tra­di­tional med­i­cine (“with no ther­a­peu­tic ben­e­fits”) or to make orna­men­tal prod­ucts. This also high­lights the need to com­bat ille­gal trade in a “much more deter­mined way.”

The above news item is reprinted from mate­ri­als avail­able at SINC via Alpha­Galileo Foun­da­tion. Orig­i­nal text may be edited for con­tent and length.

(Source: Alpha­Galileo, 11.05.2012)