302
S.P. Thrush and R.B. Whitlach
recovery dependant on habitat factors (deep/shallow and sand/mud) that are
likely to reflect hydrodynamic differences. While this finding may seem
counter-intuitive, it probably reflects problems with comparing experimental
studies that have used different disturbance techniques and have been conducted in habitats possessing different physical and biological attributes.
14.3.3 Mobility
The presence of adults and post-larval stages has been recognised in many
disturbance studies (Pearson and Rosenberg 1978; Santos and Simon 1980;
Thrush 1986; Smith and Brumsickle 1989), but the relative importance of
these life stages to recovery processes has only recently been acknowledged.
Modes of colonisation vary between species, within species associated with
different life stages, and with environmental conditions (Zajac 1991a,b;
Commito et al.1995; Shull 1997). Gunther (1992) provided a conceptual model
of the relative importance of different life stages in recolonisation dependent
on the size of the area disturbed. Due to variation in the dispersal and
mobility of different life stages, the model predicts dispersal of adults will
occur over smaller spatial scales than post-larvae, which, in turn, will be
restricted to smaller scales than larvae. Whitlatch et al. (1998, in press) used
demographic models to investigate the impact of colonisation by different life
stages of the spionid polychaete Polydora corn uta on the rate of population
recovery in a disturbed patch in cyberspace. The model revealed that lifestage effects on patch recovery time occurred in the following order of importance: larvae>juveniles>adults. However, the life stages did interact: for
example, when larval recruitment was at its maximum, colonisation by
juveniles still improved patch recovery time. Essentially, the model functions
to balance density of colonists with their potential to contribute to reproduction within the disturbed patch. Some support for a scale- and life stagedependent model of recolonisation has also been presented by Whitlatch et al.
(1998) for another spionid polychaete, Boccardia syrtis. However, different
patterns of colonisation of defaunated patches by Boccardia of different sizes
did not persist throughout the recovery process, further highlighting the role
of hydrodynamics in affecting the recovery process (Thrush et al. 1996a).
14.3.4 Opportunistic Responses
The classical opportunistic response is defined as short-term high abundance
of colonists immediately following a disturbance. The absence of this type of
response in many experimental studies has been noted (Zajac and Whitlatch
1991; Whitlatch et al., in press). Zajac and Whitlatch (1991) illustrated how
S.P. Thrush and R.B. Whitlach
recovery dependant on habitat factors (deep/shallow and sand/mud) that are
likely to reflect hydrodynamic differences. While this finding may seem
counter-intuitive, it probably reflects problems with comparing experimental
studies that have used different disturbance techniques and have been conducted in habitats possessing different physical and biological attributes.
14.3.3 Mobility
The presence of adults and post-larval stages has been recognised in many
disturbance studies (Pearson and Rosenberg 1978; Santos and Simon 1980;
Thrush 1986; Smith and Brumsickle 1989), but the relative importance of
these life stages to recovery processes has only recently been acknowledged.
Modes of colonisation vary between species, within species associated with
different life stages, and with environmental conditions (Zajac 1991a,b;
Commito et al.1995; Shull 1997). Gunther (1992) provided a conceptual model
of the relative importance of different life stages in recolonisation dependent
on the size of the area disturbed. Due to variation in the dispersal and
mobility of different life stages, the model predicts dispersal of adults will
occur over smaller spatial scales than post-larvae, which, in turn, will be
restricted to smaller scales than larvae. Whitlatch et al. (1998, in press) used
demographic models to investigate the impact of colonisation by different life
stages of the spionid polychaete Polydora corn uta on the rate of population
recovery in a disturbed patch in cyberspace. The model revealed that lifestage effects on patch recovery time occurred in the following order of importance: larvae>juveniles>adults. However, the life stages did interact: for
example, when larval recruitment was at its maximum, colonisation by
juveniles still improved patch recovery time. Essentially, the model functions
to balance density of colonists with their potential to contribute to reproduction within the disturbed patch. Some support for a scale- and life stagedependent model of recolonisation has also been presented by Whitlatch et al.
(1998) for another spionid polychaete, Boccardia syrtis. However, different
patterns of colonisation of defaunated patches by Boccardia of different sizes
did not persist throughout the recovery process, further highlighting the role
of hydrodynamics in affecting the recovery process (Thrush et al. 1996a).
14.3.4 Opportunistic Responses
The classical opportunistic response is defined as short-term high abundance
of colonists immediately following a disturbance. The absence of this type of
response in many experimental studies has been noted (Zajac and Whitlatch
1991; Whitlatch et al., in press). Zajac and Whitlatch (1991) illustrated how