Chapter 29, Problem 2DAA

Who’s the Pollinator? Massonia depressa is a low-growing succulent plant native to the desert of South Africa. The dull-colored flowers of this monocot develop at ground level, have tiny petals, emit a yeasty aroma, and produce a thick. jellylike nectar. These features led researchers to suspect that desert rodents such as gerbils pollinate this plant. To test their hypothesis, the researchers trapped rodents in areas where M. depressa grows and checked them for pollen. They also put some plants in wire cages that excluded mammals, but not insects, to see whether fruits and seeds would form in the absence of rodents. The results are shown in FIGURE 29.20.

A The dull, petalless, ground-level flowers of Massonia depressa are accessible to rodents, who push their heads through the stamens to reach the nectar at the bottom of floral cups. Note the pollen on the gerbil’s snout.

Type of rodent	Number caught	# With pollen on snout	# with pollen in feces
Namaqua rock rat	A	3	2
Cape spiny mouse	3	2	2
Hairy-footed gerbil	A	2	A
Cape short-eared gerbil	1	0	1
African pygmy mouse	1	0	0

B Evidence of Visits to M. depressa by rodents.

	Mammals allowed	Mammals excluded
	access to plants	from plants
Percent of plants that set fruit	30.4	4.3
Average number of fruits par plant	1.39	0.47
Average number of seeds per plant	20.0	1.95

C Fruit and seed production of M. depressa with and without visits by mammals. Mammals are excluded from plants by wire cages with openings large enough for insects to pass through. Twenty-three plants were tested in each group.

FIGURE 29.20 Testing pollination of M. depressa by rodents.

2. Would this evidence alone be sufficient to conclude that rodents are the main pollinators for this plant?