To elucidate the impact of browsing by moose on the indigenous insect community, we investigated the abundance of a specialist insect herbivore (galler;
Paradiplosis tumifex) and its natural enemy ...(inquiline;
Dasineura balsamicola) on balsam fir saplings in the field using exclosures in Newfoundland, Canada. The number of current-year shoots on each sapling, but not the density of balsam fir saplings, was significantly higher inside exclosures, where moose had been excluded for 9–12
years, than outside exclosures. Current-year shoots were longer and contained more, but smaller, needles inside than outside exclosures. Moose browsing had a negative impact on the abundance of both the galler and its natural enemy. Gall density was 85.6% and 60.4% lower in 2006 and 2007, respectively, outside than inside exclosures. Similarly, the attack rate of
D. balsamicola was 76.5% lower outside than inside exclosures in 2007. The apparent survival rate of
P. tumifex larvae was similar outside and inside exclosures due to higher rates of unexplained mortality in galls outside exclosures. Survival of
P. tumifex larvae was positively related to shoot length and inversely related to gall density. Only gall density was negatively related to
D. balsamicola survival. Our results demonstrate that a large mammal can cause strong bottom-up trophic cascades.
Um den Einfluss der Beweidung durch Elche auf die indigene Insektengemeinschaft aufzuklären, untersuchten wir die Abundanz eines spezialisierten Herbivoren, des Gallbildners
Paradiplosis tumifex, und seines Antagonisten, des Inquilins
Dasineura balsamicola, auf jungen Balsamtannen im Freiland und nutzten dafür Ausschlussflächen auf Neufundland, Kanada. Die Anzahl der diesjährigen Triebe auf jedem Jungbaum, aber nicht die Dichte der Jungbäume, war innerhalb der Einzäunungen, von denen Elche neun bis zwölf Jahre ausgeschlossen waren, signifikant höher als außerhalb. Die diesjährigen Triebe waren auf den Ausschlussflächen länger und besaßen mehr, aber kleinere Nadeln als außerhalb. Die Beweidung durch Elche hatte einen negativen Einfluss auf den Gallbildner und den Inquilin. Die Gallendichte war außerhalb 85,6% (2006) bzw. 60.4% (2007) geringer als innerhalb der Einzäunungen. Der Befall durch
D. balsamicola war 2007 außerhalb 76,5% geringer als innerhalb. Die apparente Überlebensrate der
P. tumifex-Larven war aber innerhalb und außerhalb der Ausschlussflächen ähnlich groß, was auf höhere Raten ungeklärter Mortalität außerhalb der Einzäunungen zurückzuführen ist. Das Überleben von
P. tumifex war positiv mit der Trieblänge korreliert und negativ mit der Gallendichte. Die Überlebensrate von
D. balsamicola war allein und negativ mit der Gallendichte korreliert. Unsere Ergebnisse zeigen, dass ein Großsäuger starke trophische bottom-up Kaskaden verursachen kann.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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