Biology Reference
In-Depth Information
seasonally variable and can also be important in mammal diets; examples are
the sap and polysaccharide gums utilized by vervet monkeys (Wrangham &
Waterman, 1981) and marsupial sugar gliders (Smith, 1982).
The review by Carthew and Goldingay (1997) cites 59 non-flying mam-
mal species known to visit flowers regularly for nectar or pollen. The inter-
action is best known from the southern continents, especially Australia,
where many marsupial species such as pygmy possums, sugar gliders, and
the honey possum (Armstrong, 1979) regularly visit the generalized brush
flowers of
Eucalyptus
(Myrtaceae) and
Banksia
species (Proteaceae)—also
visited by birds and insects—and flower products are often an important die-
tary component for the animals. Rodent pollination of
Protea
species (also
Proteaceae) occurs in similar ecosystems in South Africa, where the relation-
ship between rodents and
Protea
species has been described as non-co-
evolved (Wiens et al., 1983). This opinion was based on the brief flowering
seasons and limited plant distributions, as well as the contrast between the
morphologically specialized plants and generalist mammals. Primates may
be observed easily, but small, nocturnal pollinators are difficult to study, and
unfortunately there is often only circumstantial evidence for their role in pol-
lination (Carthew & Goldingay, 1997). Based on more quantitative evidence,
Fleming and Nicolson (2002) concluded that small mammals are responsible
for about half of the effective seed set in
Protea humiflora
, and that its nectar
and pollen are a significant nutritional resource, although limited in time and
space.
The marsupial honey possum,
Tarsipes rostratus
, weighs about 9 g and is
unique in being the only terrestrial mammal to feed exclusively on nectar
and pollen. In southwestern Australia, isotopic turnover studies in free-living
honey possums have shown that they are able to maintain energy balance
on daily intakes of 7 ml of
Banksia
nectar and 1 g of pollen (Bradshaw &
Bradshaw, 1999). The resulting nitrogen intake far exceeds the low nitrogen
requirements of honey possums measured in the laboratory (Bradshaw &
Bradshaw, 2001), so their diet does not appear to be deficient in protein.
5
WHAT HAPPENS TO NECTAR DURING
POLLINATOR SHIFTS?
Adaptive radiation within plant genera is often attributed to shifts between
pollination systems, and these can be linked to the energetic relationships
between flowers and pollinators. For example, Raven (1979) examined pol-
lination systems in the Onagraceae, concluding that shifts to higher reward
