Is "aggregate percentage" still a valid term in ecology?
The formula of "aggregate percentage" that you show is just the arithmetic mean of percentages, and I suspect that no special term is used in most studies that use mean percentages as a measure of e.g. prey composition in a certain predator (as seems to be the case in your example).

When searching for studies I think you will have more luck with using "mean prey percentages", "prey percentages" or "mean percentage composition". For instance, see Shoup &amp; Lane (2015) which includes the text (with my emphasis):


  Results of regressions correlating Secchi depth (mm) with prey percentages by weight in the stomach contents of Largemouth Bass sampled from Boomer.


Also (Ahlbeck et al, 2012):


  For each of the 25 individuals in each size class, the diet composition was calculated as the mass percentages of different prey, and then the average mass percentages were calculated for the size class.
  [...]
  prey percentages were first calculated for each fish separately and then averaged over all individuals in the sample (Hyslop 1980).


Finally, Ledger &amp; Hildrew (2008):


  Mean percentage composition (food category area as percentage total particle area) of faecal pellets of N. pictetii nymphs fed biofilm from four acid streams and four circumneutral streams.