The other day I received an email with an attached video showing scenes of a crow and a house cat frolicking and carrying on in a playful and friendly manner. Strange as it would seem, these two normally antagonistic creatures were boldly defying nature in a peaceful, even affectionate, fashion. Or at least defying nature as we typically recognize it.
It doesn't stop here however. A quick search shows all sorts of strange pairings having been captured on video, from an orangutan with a dog, to a lioness cavorting with a young antelope of all things. Relationships in nature, it would appear, are not always easy to categorize.
Biologists - like all humans for that matter - tend to want to attach labels to things. This provides an abbreviated approach for explaining various phenomena plus it gets everyone on the same page. Consider for a second, how cumbersome it would be to introduce a certain organism without the simplistic beauty of Linnaeaus's taxonomic binomials. Instead of, "a rather small, rodent-like, acorn-gathering critter with an overall grayish appearance and a bushy tail, with a tendency to escape by climbing trees," we can simply say Sciurus carolinensis, or gray squirrel.
Somewhat similarly, natural relationships are described with labels. Most of us might recall the word symbiosis from our high school biology class. In a very broad sense, the word means any close relationship between two different species of plant or animal. More narrowly, it carries the caveat that both species must benefit from the relationship. Today, most biologists seem to prefer the term mutualism in this case. A typical example of mutualism might be the beneficial gut bacteria found in our stomachs. These microbes would not survive without us and we certainly benefit from their activity by breaking down certain foods for us. It's a win/win.
Parasitism is another form of symbiotic relationship. In this case, however, one species benefits while the other is harmed. Myriad examples exist but perhaps one with local prominence is best. Mosquitoes and humans: Little needs to be spelled out who the winners and losers are in this relationship.
Still another subset of symbiosis is something called commensalism. This is where one species benefits while the other is neither harmed nor helped. A spider building a web on a plant might be a working example of commensalism where the spider is benefiting while the plant is neutrally engaged.
Biology gives us one last relationship, amensalism, where one organism is inhibited or completely erased while the other is unaffected. In this case, think of the black walnut tree (Juglans nigra) exuding a root chemical called juglone which inhibits plants from growing nearby.
Now that we've covered terms which we were all exposed to at one time or another, let me introduce a word I'd never heard of until this week: Autolycism. While not technically a "relationship" subject, it was close enough to bring into this discussion.
Autolycism was a term coined by Richard Meinertzhagen, a British ornithologist. It's meant to describe the relationship between birds and, well, "stuff" around them. It can be reasonably defined as birds making use of opportunities provided by the activities of the animals or humans around them. To illustrate, consider the great crested flycatcher which typically incorporates snake skin into its nest. Another example might be house sparrows eating smashed bugs off the grille of a parked car. Still another might be that American robin which follows you and your tiller around the garden and eats the newly exposed earthworms.
Reasonable people can argue over the fine points of these definitions, even which category to assign certain relationships, but thoughtful debate has always been a cornerstone of science. At least it should be.
I don't think we need to get ourselves into contortions contemplating such relationships, although as purely academic exercises they can be fun. Still, a part of me wonders whether it's a case of simply fulfilling our innate need to give something a category or label. Biologists surely oppose abandoning longstanding terms such as amensalism, after all they do serve a purpose. Yet for us average citizens, it might be best to simply cast a smile at the broad range of possibilities nature provides and marvel at the wonder of it all.