6 Acorn Ecology
Daniel Siscart, Victoria Diego and Francisco Lloret
6.1 Introduction
The significance of acorn production in holm oak forests can be addressed at
different levels. At the individual tree level it is one of the final results of the
classical trade-off between reproductive and vegetative effort (Bazzaz and
Ackerly 1992; Stearns 1992). Although an iteroparous, long-living species
may integrate over all its life the consequences of interannual environmental
variability on individual fitness, the pattern of seed production is expected to
reflect a balance between the losses of growth potential and the gains of sexual reproduction and dispersal success (Stearns 1992). Another related tradeoff refers to the relationship between acorn size and seedling fate. A generally
positive relationship between both parameters is expected, although interactions with other environmental factors, such as water availability, may be important (Rice et al. 1993). This individual scope can be expanded to the
population level, in which fruit production is an essential component of
population dynamics because both long-term persistence of populations and
colonization of new locations will depend on seed availability (Fenner 1992;
Crawley and Long 1995).
Acorns are also important components of food webs in oak forests because of their large size and easy consumption by many animals. Acorn predation by mammals (Felhamer et al. 1989; Jedrzejewska et al. 1994), birds
(Hannon et al. 1987; DeGange et al. 1989; Servello and Kirkpatrick 1989;
Johnson et al. 1993), and insects (Hails and Crawley 1991) has been widely
studied in relation to the population dynamics of these animals, many of
which have been shown to be dependent on the acorn crop. Some secondary
metabolites, such as tannins and phenolic substances, have been shown to act
as chemical defences in the acorns of oaks (Basden and Dalvi 1987; Steele
et al. 1993). Although studies on the food web associated with holm oak
(Quercus ilex L.) acorns are few and partial (Ruperez 1957; Tellerfa et al.
1991), acorn availability may be specially important in montane holm oak
forests, such as those of our experimental areas at Montseny and Prades (NE
Spain; Chap. 2), because of the low diversity of food sources for consumers.
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999
Daniel Siscart, Victoria Diego and Francisco Lloret
6.1 Introduction
The significance of acorn production in holm oak forests can be addressed at
different levels. At the individual tree level it is one of the final results of the
classical trade-off between reproductive and vegetative effort (Bazzaz and
Ackerly 1992; Stearns 1992). Although an iteroparous, long-living species
may integrate over all its life the consequences of interannual environmental
variability on individual fitness, the pattern of seed production is expected to
reflect a balance between the losses of growth potential and the gains of sexual reproduction and dispersal success (Stearns 1992). Another related tradeoff refers to the relationship between acorn size and seedling fate. A generally
positive relationship between both parameters is expected, although interactions with other environmental factors, such as water availability, may be important (Rice et al. 1993). This individual scope can be expanded to the
population level, in which fruit production is an essential component of
population dynamics because both long-term persistence of populations and
colonization of new locations will depend on seed availability (Fenner 1992;
Crawley and Long 1995).
Acorns are also important components of food webs in oak forests because of their large size and easy consumption by many animals. Acorn predation by mammals (Felhamer et al. 1989; Jedrzejewska et al. 1994), birds
(Hannon et al. 1987; DeGange et al. 1989; Servello and Kirkpatrick 1989;
Johnson et al. 1993), and insects (Hails and Crawley 1991) has been widely
studied in relation to the population dynamics of these animals, many of
which have been shown to be dependent on the acorn crop. Some secondary
metabolites, such as tannins and phenolic substances, have been shown to act
as chemical defences in the acorns of oaks (Basden and Dalvi 1987; Steele
et al. 1993). Although studies on the food web associated with holm oak
(Quercus ilex L.) acorns are few and partial (Ruperez 1957; Tellerfa et al.
1991), acorn availability may be specially important in montane holm oak
forests, such as those of our experimental areas at Montseny and Prades (NE
Spain; Chap. 2), because of the low diversity of food sources for consumers.
Ecological Studies, Vol. 137
Ferran Roda et al. (eds) Ecology of Mediterranean
Evergreen Oak Forests
© Springer-Verlag, Berlin Heidelberg 1999