I just returned from the 6th International Colloquium on Arboreal Squirrels, held in
Attendees of the 6th International Colloquium on Arboreal Squirrels held in Kyoto, Japan
Kyoto Japan. Besides having an amazing experience and meeting wonderful new colleagues and reconnecting with current ones (also wonderful), I was stimulated to think once again about biodiversity and ecosystem services at a global scale. Here was a conference dedicated solely to a group of small mammals (squirrels), attended by 60 researchers from around the world including countries such as Korea, Taiwan, Italy, United Kingdom, Thailand, India, Finland, Canada, Japan, and the United States.
Why the interest in small mammals, and in this case, squirrels specifically? To gain insight regarding
Lesser long-nosed bat pollinating a cactus. Photo from USFS
this question, think for a moment about the world without small mammals. You may be thinking to yourself, “hmmm, I would miss the cute squirrels in the park but otherwise no big deal – I hardly see small mammals anyway”. Because small mammals (mammals weighing less than 5kg) are mostly cryptic (hard to see or find) due to camouflage, nocturnal activity patterns, and relative shyness, many do not appreciate the services they
Harvest mouse (Reithrodontomys spp) - a seed disperser. Photo by Jean-Louis Klein and Marie-Luce Hubert
A kangaroo rat (Dipodomys spp.) - a seed storer and disperser
Arizona pocket mouse (Perognathus amplus) - a seed diserser. Photo from eNature.com
provide. Around the world, small mammals act as pollinators, seed dispersers, support forest regeneration and maintain forest health, aerate soil and allow for increased plant diversity, control insects, provide food for people and other carnivores, provide fur and pelts, provide recreational opportunities in the form of hunting and wildlife viewing, and have an aesthetic value to many. All of these services are known as ecosystem services. An ecosystem service can be thought of as services provided by an ecosystem and component species therein that are beneficial to humans and to life on earth in general. For example, healthy wetlands filter and purify water, and forests serve as carbon sinks which reduce the negative impacts of carbon emissions, provide food, habitat, medicines, and even generate their own climate. Ecosystem services provided by small mammals alone are probably worth billions of dollars, if such services could be accurately quantified. As just one small example, nearly all of human agriculture and plant production relies on insect, bird, or small mammal pollination!
Ecosystem services from tree squirrels –
Tree squirrels, just one group of small mammals, by themselves provide a multitude of ecosystem services. Some of their most important services can be attributed to their close association with forests throughout the world. Squirrels have been around for a long time – roughly 35 – 40 million years – with very little changes in their general morphology, indicating that features squirrels possessed 35 million years ago are still working well for them today. The evolutionary history between forests and squirrels goes way back, long before humans showed up on the scene (about 6 million years ago), so it is not surprising that forests and tree squirrels have co-evolved some intricate
Eastern gray squirrel caching tree seeds - Photo Mark Baldwin
codependencies such that forests depend on squirrels for a variety of services and tree squirrels are likewise dependent upon forests for food, shelter, reproduction, and survival. Many tree squirrels exhibit caching behavior, and store tree seeds and cones for later consumption. Not all of these stored seeds are actually consumed and the squirrels actually help facilitate the germination of many new trees, such as
oaks, chestnut, hickory, and many coniferous species.
Another service tree squirrels perform is via mushroom consumption, or mycophagy. Mushrooms serve as major food items for many squirrel species. Squirrels consume the entire mushroom fruiting body, spores and all, in addition to storing
Conifer seedling and associated mycorrhizae
mushrooms in trees to dry. Either by consumption or storage, squirrels help mushrooms disperse spores in the air and via feces. Many of these mushroom species form mycorrhizal associations with trees in a relationship known as a mycorrhizal symbiosis, where the tree provides fungi with carbon derived from photosynthesis, while fungi provide trees with improved nutrient uptake and the ability to acquire nutrients not readily available to the tree. Studies have shown that seedlings grown with mycorrhizal associations grow faster and do better in general compared to seedlings grown without mycorrhizal associations.
Tree squirrels also support food webs within forest
A squirrel being depredated by a hawk
ecosystems by providing food for other species like avian and mammalian predators. In short, tree squirrels help support forest ecosystem functioning in many ways and forests inhabited by squirrels are healthier and more diverse than those without.
When we think about the diversity of small mammals, including squirrels, around the world, there is hardly an ecosystem that does not benefit from services provided by small mammals, each species with their own suite of services related to the particular landscape it inhabits. Thus it is a self-perpetuating cycle: small mammals provide services to the ecosystem in which they are intricately a part of, and in turn receive many benefits themselves.
How can we begin to value ecosystem services?
Humans are a big part of ecosystems world-wide, and yet our economies generally do not recognize ecosystem services as currency. We tend only to focus on individual ecosystem products (or natural resources) like agriculture, timber, livestock, or wild game instead of valuing the system as a whole. Because of this, it is hard for us to really value conservation, because it often doesn’t make money “right now”. But at what future cost? As landscapes are broken up by development, mining, forestry, and oil exploration, oceans overfished and polluted, climate altered by unprecedented levels of greenhouse gas emissions, species lost to exceedingly high rates of extinction, how will these changes impact living species (including humans), the ecosystems they inhabit, and the services these ecosystems provide?
Japanese giant flying squirrel "Musasabi" (Petaurista leucogenys)
Increasingly we are beginning to try putting value on ecosystem services – and paying for these services proactively is likely to improve and maintain human health and well being into the future. Scientists study the unique role that various taxa play in ecosystem functioning and are beginning to think more broadly about what these various roles may mean in terms of conservation value, and what might the impacts be should such services be lost.
Small mammals are the most numerous group of mammals on earth (90% of the 5,416 known mammal species) and provide services
Japanese flying squirrel, Pteromys momonga
that are invaluable to ecosystem functioning. Most species of small mammals are rarely studied and new species are still being discovered. It is therefore important to focus research efforts on small mammals at a global scale, including tree squirrels which are so important to healthy forest functioning and so at risk from forest clearing and fragmentation. At every step we should think about what might be lost without services provided by these species, how ecosystems would be impacted, how predatory species would be affected, how plant communities would be affected. So the next time you ask a squirrel, pocket gopher, woodchuck, pack rat, dormouse, pika, kangaroo rat, or bat “what have you done for me lately?”, the answer is “a lot”.
“A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise.”
― Aldo Leopold, A Sand County Almanac: With Other Essays on Conservation from Round River