This fall I let my dog Tazz outside to roam around in the backyard. When he returned I noticed that the little troublemaker had found a way to cover himself in burrs and other seeds. A thorough brushing later and he was free of his prickly cargo. It also served to raise my curiousity about the ways plants use animals in seed dispersal. What better way for me to share and learn about this topic than with a blog post?
Seed dispersal provides several benefits to plants. For one, it allows seeds to travel further from the parent plant, which increases survivorship (due to density-dependent interactions). Second, it allows seeds to be distributed in a range of locations, some of which may be more favourable for juveniles than that of the parent. Seed dispersal can also bring plants to colonize vacant or new geographic areas, increasing the available distribution of that species.
(Courtesy of Cornell University’s Naturalist Outreach Program)
The dispersal of plant seeds by animals is known as zoochory. Plants and animals have cohabitated for millions of years in a variety of conditions, resulting in a great variety of seed dispersal adaptations. These include epizoochory, endozoochory, myrmecochory, and others.
Epizoochory is the transport of plant seeds on the outside of vertebrates, usually mammals, through adaptations such as adhesive mucus, hooks, spines, and barbs. This is the type of seed dispersal Tazz likes to regularly partake in! It is a rare adaptation in plants (~5% prevalence), but it is an effective one, as it can help plants to disperse their seeds over vast distances. There is also evidence that epizoochory aids in the rapid spread of non-native plant species.
(An example of epizoochory, courtesy of Wikimedia Commons)
Endozoochory is the dispersal of seeds by the ingestion of vertebrates (typically birds and mammals), and is most common among tree species. As many as 90% of tropic trees depend on this method of dispersal! This mutualism has plants provide tasty fruit for the animals, while the animals excrete the seeds, dispersing them in turn. This adaptation is especially important for plants with large seeds, which depend on larger animals such as chimpanzees and tapirs for dispersal. Tazz does like his fruits, maybe he provides this service to plants too…
(An example of endozoochory, courtesy of Sindri Skulason)
Myrmecochory is the movement of seeds by ants. Ants are attracted to the plants for the elaiosomes – fleshy structures rich in lipids and proteins found attached to their seeds. Ants pick up the seeds along with their attached elaiosome, consuming the nutrient lipids and proteins and moving the seeds to a disposal area. The uneaten seeds eventually germinate, completing the mutualism. While I initially thought this interaction to be unusual, it turns out as many of 9% of angiosperms take advantage of it!
(An example of myrmecochory, courtesy of Benoit Guenard)
Seed predators provide the last method of animal dispersal I’ll be covering in this post. Birds and rodents (such as squirrels) often hoard seeds for their later consumption. It is not uncommon for the hoarders to forget of their caches, leading to the germination of forgotten seeds.
(An example of dispersal by seed predators, courtesy of Gilles Gonthier)
Thank you for reading my blog post, I hope Tazz and I were able to teach you some fun facts about seed dispersal!