J. Pastor et al., Further development of the Spalinger-Hobbs mechanistic foraging model for free-ranging moose, CAN J ZOOL, 77(10), 1999, pp. 1505-1512
Citations number
20
Categorie Soggetti
Animal Sciences
Journal title
CANADIAN JOURNAL OF ZOOLOGY-REVUE CANADIENNE DE ZOOLOGIE
Spalinger and Hobbs proposed a mechanistic model of forage intake based on
the mutually exclusive actions of biting and chewing. A necessary consequen
ce of this model is that an animal postpones the intake of more food by bit
ing when it is processing food by chewing. In previous work, the Spalinger-
Hobbs model successfully predicted short-term intake in controlled experime
nts. Application of the model to an entire foraging bout requires the follo
wing assumptions: (i) biting and chewing are independent events; (ii) there
are no periodicities in the length of consecutive bite or chew sequences;
(iii) the average bite size is constant; and (iv) the bite rate does not ch
ange with the number of bites in the sequence. To test these assumptions, w
e videotaped entire foraging bouts of two free-ranging moose (Alces alces)
feeding on dense swards of Epilobium angustifolium in midsummer. From these
videotapes, we measured the time spent biting and chewing, the rates of bi
ting and chewing, the frequency distributions of consecutive bite and chew
sequences, and lengths of E. angustifolium shoots above the point of croppi
ng. Plant samples were collected in order to determine bite mass. A total o
f 1050 bites and chews were analyzed for moose 1 and 1925 bites and chews f
or moose 2. For both moose, three chewing events occurred, on average, for
each bite event. Given this 1:3 bite:chew ratio, the frequency distribution
s of consecutive bite and chew sequences were as expected from a geometric
distribution of independent events. There were no time-series correlations
or dominating frequencies in the lengths of bite and chew sequences. These
findings fulfill the first three assumptions required to extend the Spaling
er-Hobbs model to entire foraging bouts. However, the fourth assumption was
not fulfilled, in that time spent per bite increased asymptotically with b
ite-sequence length. We therefore incorporated the effect of bite-sequence
length on bite rate into the Spalinger-Hobbs model. The new model predicts
that to simultaneously maximize the marginal intake rate with respect to bo
th bite rate and bite mass, a moose should take single bites most often and
bite mass should be approximately 3.6 g. Eighty-two percent of bite sequen
ces were composed of single bites for both moose, and we and others indepen
dently observed a bite size of 3.24-3.75 g for free-ranging moose. These ob
servations lend credibility to our modified model.