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I'm reading an article that talks about morphospace and niche expansion or packing.

Differences in slope above and below zero indicate dominance of morphospace expansion versus morphospace packing, respectively.

What do the terms mean? What's the difference?

The way I understand it is that morphospace expansion is the change in morphology from the perspective of a population, but morphospace packing is, from the perspective of the ecosystem, the process where organisms are occupying the ecosystem space entirely so that no niche are available anymore. Is that correct?

The "packing" seems to refer to the density of the different "regions" of morphospace. Or said differently, you could "pack" different morphotypes in an environment. Is this a probable explanation?

I haven't found an answer looking at the history and definitions of niche.

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You're almost there--both terms concern the relationship between increases in species richness and morphological diversification. They're two opposing patterns:

Morphospace expansion indicates that a lineage is occupying new areas of morphospace with increasing species richness. (The slope is more or less relating density of morphospace occupation to speciation rate--so > 0 means new species tend to go farther away in morphospace.)

Morphospace packing indicates that a lineage is not expanding its morphospace with increasing species richness, so the existing region of morphospace that it occupies is getting more densely filled, instead of expanding.

The relationship between functional/ecological diversity and morphological diversity isn't always clear cut, though, so you have to be careful when relating the two. If you're going to use these concepts, especially if you're going to use morphological diversity as a proxy for functional diversity, it's best to state that assumption outright.

This paper includes a nice discussion of the two concepts (and is cited by the one you list): http://rspb.royalsocietypublishing.org/content/283/1822/20152013

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  • $\begingroup$ Thanks! As a quick question, are you saying that niche expansion is the same thing as morphospace expansion and same for packing? $\endgroup$
    – M. Beausoleil
    Apr 1, 2017 at 15:30
  • $\begingroup$ Not quite -- niche expanision/packing are the same base ideas, but for ecological niche instead of morphology. I'm generally pretty careful about being explicit when relating one to the other. So, for niches: Niche expansion = exploring/ expanding to new areas of niche (ecological diversity)-space with increasing species richness Niche packing = filling in the existing area of occupied niche space with increasing species richness. Does that make sense? $\endgroup$
    – Kara
    Apr 1, 2017 at 17:09
  • $\begingroup$ Yes! And it would be equivalent to say that morphospace expansion is the extension of the previous (before expansion) trait distribution to new phenotypes whereas packing would be the development of of already existing phenotypes, but increasing their density. Is that ok? $\endgroup$
    – M. Beausoleil
    Apr 1, 2017 at 18:08
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    $\begingroup$ Precisely! You've got it! $\endgroup$
    – Kara
    Apr 1, 2017 at 18:42

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