Sunday, April 11, 2010

Phylogenetically structured variance in felid bite force II

A while back I attempted to introduce my recent publication. But of course as always I think I got carried away with the phylogenetic aspect of it. So unless I hear otherwise I shall suspend my fascination with phylogenetic signals and here discuss a bit about another interesting aspect of my paper on cat bite forces.

I've discussed bite force a lot in the past so I need not introduce it any more. One idea that is fairly widespread is that bite force is somewhat correlated with ecology and in particular prey preference. This can include dietary categories (hypercarnivorous, omnivorous, etc) or prey size categories (small prey hunter, large prey hunter). Previous studies have indicated that relative bite force (after adjusted for size) seem to have a correlation with prey size categories (Wroe et al., 2005; Christiansen & Wroe, 2007). Other craniodental morphofunctional characters also seem to have some correlation with prey size (Meachen-Samuels & van Valkenburgh, 2009). However, surprisingly, my results indicate that in felids relative bite force does not have any correlation with relative prey size. This does not mean that previous studies are in error in any way, but merely that I got a different result, probably because of the differences in data treatment and methodology. I was kind of surprised and a bit disappointed honestly with my results because it would have made an easier paper if relative bite force and relative prey size were in agreement with each other. But that was not the case; and perhaps it's more exciting that they betrayed my expectations.

So cats that bite harder than expected for their sizes do not necessarily take on prey that are relatively larger than them, and vice versa. This indicates to some extent that biting ability does not govern prey killing ability. A cat with an average bite force can kill prey that is up to 10 times its own body weight. This includes the Lynx and the Clouded Leopard, both having average bite forces but able to kill very large prey. There is still a lot that we don't know about the hunting behaviours of the Clouded Leopard so I shan't mention any more about this cat, but the observation that relative bite force and relative prey size don't match up for most of the cats is saying something. I think that relative prey size is not a controlling factor of relative bite force and that relative bite force does not necessarily represent a biomechanical adaptation for killing ability (but only with respect to relative prey size of course).

OK - I lied, I shall mention phylogeny here again. What I find more interesting however is that the relationship between relative bite force and phylogeny is, while statistically significant, actually not so strong. This means that closely related taxa don't necessarily have close values in relative bite force. In other words, relative bite force doesn't show a particularly strong phylogenetic signal (although statistically significant). The most interesting thing about this is that this is consistent to some extent with the idea that functional (biomechanical) adaptations are free of phylogenetic constraint and conform more to an adaptive form of evolution. So although relative bite force may not be explained by relative prey size, there is still the possibility that it is correlated with some other form of predatory behaviour, for instance mode of prey killing or average biting time, etc.


Ville Sinkkonen said...

Very interesting. Is there any correllation between biteforce and preferred type of killing bite?
(nape bite, suffocation)

Raptor's Nest said...

Hi Ville,

That, I think, is exactly the sort of things that we should be investigating next. As far as I am aware, no such study exists. Many cat species are understudied so that kind of data may be difficult to come by. But I don't know for certain because I had not looked at those factors.