Two common finch species found on the Galapagos Islands in the equatorial Pacific Ocean are the Medium Groundfinch (Geospiza fortis) and the Small Groundfinch (Geospiza fuliginosa). Both species consume seeds of grasses, herbs, and shrubs as their primary food source. The ability to manipulate and crack the seeds is related to the size and shape of the beaks of these birds.

The two species co-occur on most islands of the Galapagos archipelago. However, on a few of the smallest islets only one or the other occur in isolation. G. fortis is the only ground finch found on the islet of Daphne. G. fuliginosa is the only ground finch species found on the islet of Los Hermanos.

Question 12

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The data shown above reveal that:

1) The fundamental niche of G. fortis spans seeds from blank , and its realized niche from blank . G. fortis cannot feed on the blank seed types. Additionally, it avoids feeding on the blank seed types as long as enough of the blank seed types are still available. This is consistent with the hypothesis that G. fortis initially avoids seeds in its fundamental niche that blank and hence make less energy available to them for the same amount of time spent feeding.

2) The fundamental niche of G. fuliginosa spans seeds from blank ; and its realized niche from blank . G. fuliginosa cannot feed on the blank seed types. Additionally, it avoids feeding on the blank seed types as long as enough of the blank seed types are still available. This is consistent with the hypothesis that G. fuliginosa initially avoids seeds in its fundamental niche that blank and hence make less energy available to them for the same amount of time spent feeding.