T

he distribution offitness-limiting resources
is often suggested to be of great importance in the
evolution of social and mating systems (Emlen and
Oring 1977). Male reproductive strategies often are di-
rectly related to distribution of receptive females; female
distribution is influenced by food resources, nest availabil-
ity, and risk of loss of juveniles (Lott 1991; Boag and Wig-
gett 1994a; Wolff and Peterson 1998). Given variation in
resource distribution and efficacy of individuals in accessing
resources, intraspecific variation in tactics used to access re-
sources is predicted to occur.
Alternative reproductive tactics were described for a di-
verse array of animals (Cade 1980; Dunbar 1982; Dominey
1984; Caro and Bateson 1986; Gross 1996; Brockmann
2001). Tacticrefers to the phenotype that results from a
strategy(Gross 1996; Brockmann 2001). Game-theoretical
approaches to understanding adaptive value of behavioral
tactics provide a powerful intellectual framework and have
led to important insights into evolution of alternative tac-
tics (Maynard-Smith 1982; Parker 1984a). Alternative re-
productive tactics in mammals are diverse (Dunbar 1982;
Dominey 1984; Caro and Bateson 1986; Wolff, in press).
The secretive nature of most rodents makes assessing re-
productive behaviors challenging; however, alternative re-
productive tactics are reported from a number of rodents
to include ground and tree squirrels, chipmunks, and cri-
cetids (Wolff, in press). Wolff identifies three major types
of alternative tactics: (1) conditionally dependent strategies
determined by resource availability, (2) mixed evolutionary
stable strategies, maintained with equal payoffs through

frequency-dependent selection, and (3) “making the best of

a bad job,” when unable to adopt the most successful strat-

egy. Mammalian strategies appear to be primarily of this

third type, where tactics are conditional upon age, size, or

dominance rank, with younger and subordinate individuals

using a less successful tactic (Wolff, in press).

Unlike the vast majority of rodents, many tree squirrels

are large, diurnal, and have conspicuous aboveground re-

productive behaviors. Thus tree squirrels are excellent mod-

els for study of reproductive strategies and alternative repro-

ductive tactics. In this chapter, “tree squirrel” refers to a

member of the family Sciuridae that is dependent upon for-

est trees for food, nests, and cover, and thus have a signifi-

cant arboreal component to their daily life (Gurnell 1987;

Steele and Koprowski 2001). Primitive ancestors of extant

Sciuridae were arboreal or semiarboreal, similar to present-

day tree squirrels (Hafner 1984). Relatively unchanged over

35 million years, tree squirrels are considered to be living

fossils (Emry and Thorington 1982). Herein, I briefly re-

view the social systems of tree squirrels in which mating

systems are operating, provide an overview of reproductive

biology of tree squirrels, and review male and female alter-

native reproductive tactics.

Sociality in Tree Squirrels

Tree squirrels are often considered asocial, solitary mam-

mals that forage for dispersed food items; however, inter-

mediate levels of sociality are documented in numerous

Chapter 7Alternative Reproductive Tactics and

Strategies of Tree Squirrels

John L. Koprowski