Does anyone know why ticks exist? Just to propagate their own species? To provide food for some other animal? Organisms often have interdependant relationships with other organisms, but I can’t see how the world would be any different if ticks did not exist…
I don’t see why they would have to exist to provide food for some other species. Without getting into an intelligent design debate, I think you may misunderstand evolution. Species don’t come into being for the benefit of other species–each species is geared first and foremost for the survival of itself.
For example: zebras don’t exist so they can be food for lions, or so they can eat grass. Zebras exist for zebras. If there were no more zebras, lions would eat something else (or die, if all lions ate were zebras) and something else would eat grass. Maybe not right away, but unexploited ecological niches don’t last for long.
Ticks, like any other parasitic organisms (or any organisms, for that matter), exist because they a) evolved and b) are adapted to exploit the particular niche they occupy. As easy e mentions, organisms do not evolve to perform a specific ecological function, they simply evolve in a way such that they are either able to capitalize on a niche vacancy, or create a niche (note that depending on the definiton one uses, a niche may or may not exist independently from the organism(s) which occupy it).
As for the actual role of parasites, often, they seem to act as population regulators, as seen in this paper [.pdf document]: The role of parasites in the dynamics of a reindeer population. In this case, the parasite is an intestinal nematode, but ticks likely can perform much the same role.
Ticks exist to make little ticks. Making littl’uns is the reason for life itself (inasmuch as it has any reason). As for how the world is different for having ticks in it, Darwin’s Finch has given one excellent example; here’s another: ticks spread bacteria, viruses, plasmids, and other repositories of novel genetic material from organism to organism. In addition to the spread of disease, this may conceivably enhance the rate of evolution itself, raising the possibility that life on Earth might be just a little more primitive without ticks and other bloodsucking parasites.
Ticks serve two vital functions. They encourage grooming in several mammal species, and they provide sound effects for mechanical clocks and watches.
On a slightly different tack, how much worse would the world be if we could kill all ticks tomorrow? I know that mosquitoes are a food source for some birds, insects, etc., but would any other species really suffer if we erased those little vampires tomorrow?
- toadspittle, who’s running out of Off Skintastic
It’s always hard to tell what would happen if we eliminated all ticks. Several parasites would almost certainly be wiped out, which could in turn lead to explosions in other various species of animas which are currently held in check. There are poisonous tick species in various parts of the world that directly control animal numbers, perhaps the most important being the effect of ticks in eliminating huge numbers of young mammals throughout Australia and SE Asia.
It would not have any great and immediate impact on humans if we extincted all ticks, but the same could be said for elephants, humpback whales and grey wolves.
Teleology has become rather unfashionable.
I think chickens eat ticks if they get a chance.
I think chickens will eat anything if given the chance! They are actually nasty birds! But they sure taste good themselves!
Heh heh. Do ticks create a niche, or do they create an itch?
Yes, I assure you chickens will eat anything including each other.
When I was a kid we would carry a 22 rifle on the tractor to shoot the jackrabbits. Bring them in at night, skin them for the chickens…they would pick the bones clean. Maybe we were so poor we couldn’t afford chicken feed. 
They are the yin to tocks’ yang.