escape cost influence by what
Answers
Answer:
Effects of risk, cost, and their interaction on
optimal escape by nonrefuging Bonaire
whiptail lizards, Cnemidophorus murinus
William E. Cooper, Jr.,a Valentı´n Pe´rez-Mellado,b Teresa Baird,c Troy A. Baird,d
Janalee P. Caldwell,e and Laurie J. Vitte
a
Department of Biology, Indiana University-Purdue University at Fort Wayne, Fort Wayne, IN 46805, USA,
b
Departamento de Biologia Animal, Universidad de Salamanca, 37071 Salamanca, Spain, c
Oklahoma
City–County Health Department, 921 NE 23rd Street, Oklahoma City, OK 73105, USA, d
Department of
Biology, University of Central Oklahoma, 100 N. University Drive, Edmond, OK 73034, USA, and
e
Sam Noble Oklahoma Museum of Natural History and Department of Zoology,
University of Oklahoma, 2401 Chautauqua Avenue, Norman, OK 73072, USA
Optimal escape theory seeks to explain variation in the distance to an approaching predator at which the prey initiates escape
(flight initiation distance). Flight initiation distance increases when predators pose a greater threat and decreases when escape
costs increase. Although optimal escape theory has been highly successful, its predictions have been tested primarily for species
that escape to discrete refuges, and most studies have focused on single risk or cost factors. We present data from two
experiments in which two risks or a risk and a cost varied in Bonaire whiptail lizards (Cnemidophorus murinus) that escaped without
entering refuges. Our data verify several predictions about optimal escape for nonrefuging lizard prey. Two risk factors, speed
and directness of approach by the predator, interacted. Directly approached lizards had greater flight initiation distances than
did indirectly approached lizards when approached rapidly, but shorter flight initiation distances when approached slowly. Flight
initiation distance was shorter in the presence of food and during slow versus rapid approaches, but contrary to expectation, food
presence and approach speed did not interact. This would be explained if cost curves are nonlinear or if they are parallel rather
than intersecting when the predator reaches the prey. More empirical work is needed to determine which risk and cost factors act
additively and which act synergistically. The absence of interaction between the risk and cost factors suggests that cost curves were
nonlinear. Key words: antipredatory behavior, behavior, escape theory, refuge, Squamata. [Behav Ecol 14:288–293 (2003)]
Optimal escape theory (Ydenberg and Dill, 1986) predicts
that a prey should begin to escape from an approaching
predator when the predator reaches a point at which the risk
of predation equals the cost of escape. This distance from the
predator at which prey are predicted to initiate flight is the
optimal flight initiation distance. Optimal escape theory has
been strongly supported by experimental tests of the effects of
numerous risk and cost factors in a wide range of prey taxa (see
below). Effects of simultaneous variation in more than one risk
factor or in a risk factor and a cost factor have not been
considered theoretically and have received very little empirical
attention. This is surprising because prey are typically faced
with multiple risks and costs that operate simultaneously. For
example, prey should be able to respond to the dangerousness
of the predator, its speed, the distance from and security of
a refuge, the cost of giving up feeding opportunities, and other
risks and costs that may affect a single encounter with
a predator. Another aspect of optimal escape theory that has
not has been widely tested is its applicability to nonmammalian
prey that flee in the open rather than enter a refuge.
Flight initiation distance increases with magnitude of risk
for several risk factors, including dangerousness of the
predator (McLean and Godin, 1989; Walther, 1969); predator
approach speed (Cooper, 1997c), directness of the predator’s
approach (Bulova, 1994; Burger and Gochfeld, 1981, 1990;
Cooper, 1997c), direction of predator’s approach relative to
the refuge (Cooper, 1997a; Kramer and Bonenfant, 1997),
distance to nearest refuge (Bulova, 1994; Bonenfant and
Kramer, 1996; Cooper, 1997b; Dill, 1990), availability of cover
(Grant and Noakes, 1987; LaGory, 1987), persistence by the
predator (Cooper, 1997b), changes in a predator’s path to
a direct approach (Cooper, 1997b, 1998a), and lowered body
temperature that results in lower escape speed in ectotherms
(Rand, 1964; Smith, 1997).
As predicted by optimal escape theory, increases in escape
costs are accompanied by decreases in flight initiation
distance. Energetic expenditure and increased likelihood of
injury during escape have the potential to be substantial, but
are likely relatively small for prey that flee short distances to
refuges. Loss of opportunities to forage and engage in fitness-
Answer:
from escape studies is that