The Acorn Connections

Gypsy Moth defoliation and Lyme disease are major problems in eastern US oak forests. Using a combination of long-term studies and large-scale experiments, our collaborative research has shown that acorns initiate a complex series of ecological chain reactions. These interactions can ultimately determine whether or not Gypsy Moth outbreaks will occur, and can determine Lyme disease risk to people.

In this Project

Acorns are a key food for white-footed mice. The mice are key predators on Gypsy Moth pupae. When there are many acorns the mouse population increases, which keeps the moth population low. However if there are no acorns, the mouse population collapses allowing the moth population to increase. Acorns also attract white-tailed deer into oak forests to feed on acorns. The deer carry adult ticks that drop off and spend the winter in the oak forests. The next year the female ticks lay eggs that hatch into larval ticks. The larval ticks are not infected with the bacteria that cause Lyme disease, but become infected when they feed on the mice that have increased because of acorns. This means that the risk of Lyme disease can be higher in oak forests two years after a large acorn crop.

Acorns are a key food for white-footed mice. The mice are key predators on Gypsy Moth pupae. When there are many acorns the mouse population increases, which keeps the moth population low. However if there are no acorns, the mouse population collapses allowing the moth population to increase. Acorns also attract white-tailed deer into oak forests to feed on acorns. The deer carry adult ticks that drop off and spend the winter in the oak forests. The next year the female ticks lay eggs that hatch into larval ticks. The larval ticks are not infected with the bacteria that cause Lyme disease, but become infected when they feed on the mice that have increased because of acorns. This means that the risk of Lyme disease can be higher in oak forests two years after a large acorn crop.

Acorns initiate other chain reactions among species (e.g., mice, chipmunks, and songbirds; see R. Ostfeld and K. Schmidt), and Gypsy Moth defoliation has many effects on the forest, including influences on nutrient cycling (see G. Lovett). Because moth defoliation reduces acorn production, understanding how moths are able to persist in the forest amidst intense predation pressure by mice has also been a recent focus of our work. This has led us to study the roles of local dispersal of moths relative to local spatial variation in mouse predation as the primary determinants of moth persistence (see B. Goodwin, E. Schauber). Recent research has shown that there are mouse hot and cold spots in the forest of varying persistence. We are now investigating how these hot and cold spots affect moths, Lyme risk and songbird nesting success.

Overall, our research is trying to understand how the complexity of interactions among species – including how they vary in space and time – affects the functioning of oak forest ecosystems with important implications for understanding forest ecosystem health, human health and biodiversity.

Fig. 1. Interactions in eastern deciduous forests influencing forest dynamics, Lyme-disease risk ("pathogens"), nesting success of some ground-nesting songbirds, and gypsy moth dynamics. Arrows indicate the direction of the effect of one taxon on another. Solid lines indicate positive effects (e.g., mast production on mice), and dashed arrows indicate negative effects (e.g., gypsy moths on oak trees). From Ostfeld & Jones, In Press.

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