Australasian Science: Australia's authority on science since 1938

All Creatures Great and Small

Photo: Si-Chong Chen

While it’s true that large animals feed on some large seeds from fleshy fruits, we shouldn’t overlook the fact that large animals, especially ungulates such as rhinoceros, zebras, peccaries, deer and buffalos, also unintentionally vacuum up huge amounts of small, inconspicuous seeds as they browse on short grassy vegetation. These interactions are the primary factor that drives the negative relationship between animal body mass and ingested seed size across all vertebrates. Photo: Si-Chong Chen

By Si-Chong Chen & Angela Moles

Many large animals are rare or under threat, so the discovery that they ingest and disperse both large and small seeds has widespread ecological consequences.

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It’s estimated that more than 90% of the plant species in tropical rainforests rely on animal ingestion to disperse their seeds. Some seeds may even need to be processed by the animals’ digestive tracts to be able to germinate.

You might think that larger creatures would gulp down bigger chunks of food. This idea had long been accepted by scientists studying seed dispersal, leading to the assumption that larger fruit-eating animals generally ingest larger seeds than smaller animals. This idea has been supported by studies of some animals, including fruit-eating birds and bats, but do these positive patterns hold true at a broader scale and across diverse taxa?

We have compiled data from thousands of scientific papers and amassed a worldwide database of 13,135 animal–seed interactions from all vertebrate groups, including 224 species of mammal, 313 species of bird, 42 species of reptile, one species of amphibian and seven species of fish.

The smallest seed-ingesting animal in our dataset was the Chatham Islands skink, which only weighs 3.3 grams. The smallest seed in its diet comes from a type of mountain snowberry. In contrast, the largest seed in the African elephant, which weighs nearly 4 tonnes, comes from an African tropical tree and is 9 cm long.

The South American tapir, which weighs more than 200 kg, transports the greatest number of seed...

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