ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
ecology of phasmids - KLUEDO - Universität Kaiserslautern
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Introduction 5<br />
population densities then reflects the impact <strong>of</strong> control. Population control factors can act pre- or postnatal.<br />
Here, I present a first estimate <strong>of</strong> egg mortality and failed hatching and show the effect <strong>of</strong> prenatal<br />
mortality on potential population increase <strong>of</strong> M. diocles.<br />
Dietary constraints <strong>of</strong> M. diocles are the subject <strong>of</strong> Chapter 4, addressing the bottom-up view <strong>of</strong><br />
herbivore regulation. Nutritious requirements <strong>of</strong> <strong>phasmids</strong> may be age or sex-specific (e.g., Cassidy<br />
1978; Sandlin & Willig 1993), and early life stages <strong>of</strong> herbivorous insects may suffer high mortality<br />
depending on the food source and its species-specific physical and chemical leaf characteristics (Joern<br />
& Gaines 1990; Belovsky & Slade 1995). In feeding-trials, I observed performance (sensu growth and<br />
survival) <strong>of</strong> first instar nymphs and preference <strong>of</strong> adult females on different host plants reflecting<br />
M. diocles host range. Performance <strong>of</strong> nymphs and preference <strong>of</strong> adults were analyzed with respect to<br />
particular defensive leaf traits that potentially reduce digestibility <strong>of</strong> the foliage or are toxic to the<br />
organism.<br />
In Chapter 5 I am concerned with the top-down view <strong>of</strong> M. diocles population regulation. In a<br />
predation-exclusion field experiment I assessed the impact <strong>of</strong> predators on first instar nymphs <strong>of</strong><br />
M. diocles. A general pattern in insects is high mortality <strong>of</strong> early life stages with high impact <strong>of</strong><br />
predation, particularly by parasitoids (Cornell & Hawkins 1995; Cornell et al. 1998). While these<br />
patterns arose from studies on holometabolous insects, knowledge on hemimetabolous herbivores<br />
mainly originates from studies on temperate grasshoppers (e.g., Joern & Gaines 1990; Belovsky &<br />
Slade 1995; Oedekoven & Joern 1998).<br />
1.3 Site characterization and general methods<br />
1.3.1 Study site, vegetation and climate<br />
The study took place on Barro Colorado Island (BCI; 9 o 09’N, 79 o 51’W), a field site <strong>of</strong> the Smithsonian<br />
Tropical Research Institute (STRI) in Panamá (Figure 1-2). The island <strong>of</strong> 1567 ha is located in the lake<br />
Gatun. This freshwater lake was dammed up between 1911 and 1914 during construction <strong>of</strong> the Panama<br />
Canal. The island is the centerpiece <strong>of</strong> the 5600 ha Barro Colorado Nature Monument (BCNM) that was<br />
established in 1978 and includes the adjacent mainland peninsulas. In 1923, BCI was declared as<br />
biological reserve and in 1946 it became a unit <strong>of</strong> the Smithsonian Institution. Since then, the island has<br />
become one <strong>of</strong> the most intensively studied areas in the tropics.<br />
BCI is completely covered with semi-deciduous tropical moist forest <strong>of</strong> several successional stages<br />
(Foster & Brokaw 1982). The northeastern part <strong>of</strong> the island consists <strong>of</strong> 100 to 200 year old secondary<br />
forest whereas old forest <strong>of</strong> 200 to 400 years covers most <strong>of</strong> the southeast <strong>of</strong> BCI. A small strip <strong>of</strong> old<br />
forest remained south <strong>of</strong> the laboratory (surrounding Lutz Creek). The area around the laboratory is<br />
cleared and the vegetation is dominated by pioneer plant species such as Cecropia, Ochroma, Trema,