Subsidy

About a week ago, while driving into work, I noticed a few Turkey Vultures (Cathartes aura) feeding in a grassland.  By itself that sighting wasn't unusual, but the exact location was a little odd — I hardly ever see vultures feeding there.  It was close to the road, so I decided to walk out to take a look at what they were feeding on.

 

I expected it to be some sort of mammal or bird...but my eyes opened wide to see this:

 

An Ocean Sunfish (Mola mola)!  The vultures were eating this Ocean Sunfish in a grassland at least 120 feet from the bluff edge!

So one of the first questions is, how did the sunfish get there?  It's seems unlikely that a vulture could lift such a large prey item.  It's more likely that the sunfish washed up on the beach, and then a mammal (e.g., Coyote?) carried it into the grassland.

As I was photographing the sunfish, I noticed some movement along one edge.  Looking more closely, I realized an insect with strong black and yellow markings was landing on a torn area of the sunfish:

 

I don't have a lot of experience identifying insects in this group, but I think this might be a Western Yellowjacket (Vespula pensylvanica).  Please correct me if I'm wrong.

The yellowjacket was actively carving out a piece of the sunfish!  Here's a sequence of images documenting the event, until just before the yellowjacket flew off with its prize:

 

 

 

This is a very nice example of a spatial subsidy — "movements of nutrients, detritus, prey, and consumers among habitats" — as defined by Gary Polis and colleagues in 1997. (See Polis, G.A., W.B. Anderson, and R.D. Holt.  1997.  Towards an integration of landscape and food web ecology: The dynamics of spatially subsidized food webs.  Annu. Rev. Ecol. Syst.  28: 289-316.)

Inspired by the work of Gary Polis, ecologists have been increasingly interested in the movement of resources and energy between distinct ecosystems — such as from the sea to the land.  In this case, the Ocean Sunfish, normally found in the open ocean, was washed up onto a sandy beach, and then probably carried by a terrestrial mammal to a coastal grassland where it then served as food for land birds (vultures) and terrestrial insects (yellowjackets).  I couldn't help wonder — how often do yellowjackets eat Ocean Sunfish in grasslands?