I hadn’t planned on writing another post until Thursday, after my next day volunteering. However I read an article today that I found really interesting and I thought I’d share it with you. It is about how the reintroduction of wolves in Yellowstone National Park has, by affecting the number of berry bearing plants, improved the diet of bears. The restoration of wolf populations has previously been acknowledged as having a positive effect on the recovery of certain tree species by controlling elk numbers that would otherwise graze on young trees but this adds another strand in what is looking like a becoming a rather complex web.
This is just one example of the many interactions that occur within a habitat. To me this stresses how absolutely vital the understanding of the ecology of an ecosystem is. Knowing the biology of a stand-alone species is all well and good but to get the whole picture each species position within the ‘community’ should be figured out (‘community’ in its ecological sense does have some debate around it as to whether it an acceptable ‘level’ at which to study ecology but the evidence I’ve seen for it is pretty convincing).
I’ve always been aware that the natural world is all interconnected, with the most obvious example being that of the predator and prey relationship. Without a sustainable source of prey, a predator just cannot survive. It was a second year ecology lecture that really brought home just how intricate these relationships can be.
The example we were given was that of all the influences that affect where a female syrphid (hoverfly) lays its eggs (may seem a slightly random organism to look at but our lecturer has a special soft spot for hoverflies as he’s been studying them since his undergraduate degrees). The hoverfly requires aphids as a food source for its larvae. Colonies of aphids sometimes have soldiers protecting them, which will attack the hoverfly larvae. The presence of these soldiers changes where a hoverfly will lay her eggs. Other aphidophages (organisms that eat aphids) may be about; they not only eat the aphids but could eat the hoverfly larvae. An example of this is ladybird larvae. Other parasitoids will attack the hoverfly larvae themselves or the aphids, and thus reduce the quality of food. Ants can be present and tend to aphids, milking the honey dew. They will attack hoverfly eggs if they can but will also drive away the parasitoids that use hoverflies as hosts so there are both benefits and downsides to their presence. As well as this some plants emit signals, when they are attacked by aphids, which attract organisms, such as hoverflies, that use aphids as food or hosts. All of these interactions are important as if the larvae are to survive they must be laid in the right place which is be influenced by any or all of those interactions. This is just one small event in the biology of the hoverfly. I think it would be fair to assume that a whole host of interactions occur at other stages throughout the hoverflies life.
(I hope that isn’t too confusing. I’ve taken it pretty much straight from an exam answer I wrote. I got ‘good summary’ in the margin next to that section which is actually high praise from a marker who would normally write about three words at the end of your exam paper)
The wolves in Yellowstone are at the middle of another of these complex webs of relationships. It seems almost strange to think that the presence of wolves would affect the number of trees or the diet of a grizzly bear but it does. It is the influence of the wolves on the number of elk population that is having this effect on the vegetation. When the wolves were not around the elk population grew and the trees suffered as new growth was eaten by the elk. The return of the wolf relaxed the pressure that the elk were putting on the trees allowing them to come back. A similar sort of effect is happening with berry bearing plants. As there are now less elk due to the predation by wolves, berry bearing plants are not being grazed so heavily meaning that more berries are available for bears to eat. This knock on affect that goes up and down the different levels of the food web is known as a trophic cascade. Wolves, elk and bears are not the full picture. Willow trees and beaver also have strands within this web but I’m not going to go into that now as it may make this too complicated and you should have the idea by now (If you are interested in how willows and beavers fit into the Yellowstone ecosystem you can read a bit about it on this blog I found by one of the researchers.
Things like this are just one of the hundreds of reasons why I find the natural world so fascinating. There is so much out there that we don’t know yet and we’re constantly being surprised and finding out new things. It also has a practical importance, especially in today’s world. Knowing the interactions between organisms in an ecosystem will play vital roles in conservation efforts. Whisking all members of an endangered species out of their disappearing rainforest and into a new protected one is not guaranteed to save them; in fact it could make the situation worse (think invasive species). There is a lot more to consider then just the species you are trying to save.
I’m not going to go off and preach here about what needs to be done for a successful conservation effort. I just wanted to draw attention to how complex and amazing the world we live in is and highlight why studying ecology, or behaviour, or any aspect of biology is worthwhile and important. It is topics like this, and the fact that there is so much more to find out, which makes me want to spend the rest of my life exploring the natural world.
P.S I apologise if I’ve got any of the facts wrong in this post. This is all pretty complicated so I’ve been trying to keep it as simple as possible so it was easy to follow. I’ll happily make any corrections if anyone spots that some need making.
P.P.S This seems to be a popular topic today. Even as I write this out (in its draft form) a story has just popped up on my twitter feed about how the loss of a single bee species can lead to a drop in seed production in plants.