44
Activity Patterns
deliberately caused in early summer. The preponderance of highly dispersive
Coleptera which on the one hand can escape fire and on the other can rapidly recolonise burnt areas was also attributed to frequent fires.
4.3
Feeding Activity
It is generally assumed that the temporal pattern of feeding activity among
terrestrial arthropods parallels variations in climatic variables. However, in
Mediterranean regions environmental thresholds determine arthropod activity. Consequently, seasonal changes do not strictly follow relevant changes in
the relative humidity and temperature of the atmosphere.
In most cases the water content of the food rather than the relative humidity of the air conditions the feeding activity of soil arthropods (Iatrou 1989).
In xeric Mediterranean habitats the water content of food has a directeffect
on feeding activity, whereas in mesic habitats the water content of food is
high in autumn and spring when feeding activity is at its highest level. Consequently, in the latter habitats temperature principally determines the onset
and ending of feeding.
In general, foraging occurs at about 7-25 DC. Feeding activity therefore
comes to a halt in winter when the mean monthly temperature is below 7°C,
and it drops drastically in summer when the ambient temperature is above
2S DC. Due to low QIO values, feeding activity also changes slightly within the
range of 7-25 0c, Seasonal changes in the feeding activity of most terrestrial
arthropods from mesic Mediterranean regions conform with the above
scheme (Bertrand et al. 1987; David 1987; Iatrou and Stamou 1989b). For
example, except when overwintering and moulting, the diplopod Glomeris
balcanica is active in Hortiatis throughout the year (Fig. 4.2). Intensive feeding was recorded after cessation of moulting in November and again during
the period of oviposition in May/June.
Changes in available water have an overriding effect on the feeding activity of epiphytic arthropods such as pollinating insects. Pollination is of decisive importance for plant reproduction in the more xeric Mediterranean formations. In fact, phryganic plants are mostly insect pollinated (Petanidou
and Vokou 1990). The great majority of pollinators are pollen consumers.
Nevertheless, in the dominant species of Labiatae pollen is limited, and dilute
nectars become the principal reward to pollinators, also representing their
main source of water (Johnson and Bond 1992). Thus, the factor determining
the activity of insects is the capability of Labiatae to provide both nutritive
and water sources, and insects have to synchronise their feeding activity with
the flowering period of plants.
In a phryganic formation Petanidou and Vokou (1993), recorded 201 insect
species visiting Labiatae, most of them Hymenoptera and Diptera. A remark-
Activity Patterns
deliberately caused in early summer. The preponderance of highly dispersive
Coleptera which on the one hand can escape fire and on the other can rapidly recolonise burnt areas was also attributed to frequent fires.
4.3
Feeding Activity
It is generally assumed that the temporal pattern of feeding activity among
terrestrial arthropods parallels variations in climatic variables. However, in
Mediterranean regions environmental thresholds determine arthropod activity. Consequently, seasonal changes do not strictly follow relevant changes in
the relative humidity and temperature of the atmosphere.
In most cases the water content of the food rather than the relative humidity of the air conditions the feeding activity of soil arthropods (Iatrou 1989).
In xeric Mediterranean habitats the water content of food has a directeffect
on feeding activity, whereas in mesic habitats the water content of food is
high in autumn and spring when feeding activity is at its highest level. Consequently, in the latter habitats temperature principally determines the onset
and ending of feeding.
In general, foraging occurs at about 7-25 DC. Feeding activity therefore
comes to a halt in winter when the mean monthly temperature is below 7°C,
and it drops drastically in summer when the ambient temperature is above
2S DC. Due to low QIO values, feeding activity also changes slightly within the
range of 7-25 0c, Seasonal changes in the feeding activity of most terrestrial
arthropods from mesic Mediterranean regions conform with the above
scheme (Bertrand et al. 1987; David 1987; Iatrou and Stamou 1989b). For
example, except when overwintering and moulting, the diplopod Glomeris
balcanica is active in Hortiatis throughout the year (Fig. 4.2). Intensive feeding was recorded after cessation of moulting in November and again during
the period of oviposition in May/June.
Changes in available water have an overriding effect on the feeding activity of epiphytic arthropods such as pollinating insects. Pollination is of decisive importance for plant reproduction in the more xeric Mediterranean formations. In fact, phryganic plants are mostly insect pollinated (Petanidou
and Vokou 1990). The great majority of pollinators are pollen consumers.
Nevertheless, in the dominant species of Labiatae pollen is limited, and dilute
nectars become the principal reward to pollinators, also representing their
main source of water (Johnson and Bond 1992). Thus, the factor determining
the activity of insects is the capability of Labiatae to provide both nutritive
and water sources, and insects have to synchronise their feeding activity with
the flowering period of plants.
In a phryganic formation Petanidou and Vokou (1993), recorded 201 insect
species visiting Labiatae, most of them Hymenoptera and Diptera. A remark-