I am not convinced any of the "ecological" explanations even begin to touch the question!
There is usually a tacit assumption that perforated leaves have evolved from unperforated leaves - hence the question 'why holes?'. But maybe they have evolved from leaves with had dissected margins - in which case the question becomes why, in their development, are these leaves dissected from within the margin instead of at the margin?
Roughly speaking, the leaf of a mature M. deliciosa has three hierarchical sets of holes - a set very big ones whose thin edges break as the leaf unfolds creating the major dissections of the leaf, a set of medium holes and a set of small holes near the midrib. Philidendron bipinnatidum on the other hand, also roughly speaking, has (up to) three sets of marginal lobes, a set of very big ones making the major divisions, which are themselves lobed (the mid-level divisions) and a few of the finest "lobes on lobes on lobes". The leaves of these two common examples are, in a sense, 'inside out' versions of each other....
Looking at it primarily as an evolution of development (interior functional) question rather than an adaptive-ecological (exterior functional) question leads one off in a rather different direction [see Hay & Mabberley in Bot. Jahrb. Syst. 113 (1991) 339-428] :-)
Date: Sat, 25 Feb 2012 20:38:10 -0800
Subject: Re: [Aroid-l] Holes
No one has figured out definitely what is the function of holes, but several ideas have been proposed in the literature. One -- which I consider the least plausible -- is to fool insects: supposedly, insects see the leaves appearing already to have been eaten and move on, as if to avoid a plant with higher concentrations of defensive compounds, or possibly competition from other insects. This theory does, however, raise questions about how important visual cues are to herbivorous insects. Another idea is that the holes increase air circulation around the leaves, possibly providing "air conditioning" or facilitating gas exchange. To me this seems more likely.
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