Believe it or not, for all the years that this show has been going on, we are having our first Gratton Lab retreat up at the Trout Lake research station. Hopefully this will become an annual event. The group is almost complete, missing only a few of the regulars (Tim and Jamin, we’ll catch you next time) and our stalwart crew of (post/)undergraduate crew. Skiing in the morning and a big meal slated tonight. Claudio
At which scale should conservation of non-crop habitat take place to sustain such important ecosystem services as the control of crop pests? To help understanding the consequences of land-use decisions, Ben Werling and Claudio Gratton examined the impact of local and broad scale landscape structure on the predation of two insect pests of potatoes in Wisconsin, the Colorado potato beetle, Leptinotarsa decemlineata, and the green peach aphid, Myzus persicae.
At a local scale (meters), potato fields of different sizes were bordered by different areas of uncultivated grassy field margins. At a broad scale (kilometers), potato fields and grassy margins were set in landscapes composed of varying percentages of non-crop habitat. The Predation of both investigated species was significantly impacted by non-crop habitats, but this relationship occurred at different scales for each pest and interacted differently with habitat type. The predation of exposed egg masses of L. decemlineata was greater in field margins than in the potato crop and increased in both habitats when field margins were large relative to the area of potatoes while that predation was less affected by the amount of non-crop habitat within kilometers. In contrast, the suppression of aphid population growth by predators increased with the area of non-crop habitat within kilometers of fields, but was less affected by the field margin area.
As a potential mechanism for the differential impact of local and broad scale landscape structure on predation of these pests, Ben and Claudio suggested that the two pests are attacked by natural enemies with different dispersal abilities. Aphid predators may move across the landscape at broader scales than predators that attack L. decemlineata eggs. Alternatively, the same predators may attack both pests, but respond to landscape structure differently in June, when L. decemlineata egg abundance peak and August when Aphids are present.
Ben and Claudio quoted that the influence of non-crop habitats on predation the potato beetles is due to the movement of natural enemies between resource-providing field margins and potatoes. Consequently small field sizes could reduce the travel distance and increase the ability of organisms to access resources in non-crop habitats. The oppositional patterns of M. persicae suppression suggest that aphidophagous predators move between non-crop habitats at the scale of kilometers. Because even a single ecosystem service, such as pest predation, can be influenced by landscape structure at multiple scales, the authors emphasize that it may be necessary to conserve heterogeneity both at the levels of individual farms and entire mosaic landscapes to maintain ecosystem services.
Demand for fossil fuels is increasing globally. The United States is pursuing an energy policy that aims to reduce our dependence on fossil fuels by expanding renewable energy sources. One important part of this effort is the use of bioenergy crops to produce heat, electricity, and transportation fuel. Meeting energy demands could have big implications for agricultural land use. Not only will land used to grow fuel not be available for growing food, but the choice of energy crop will have large consequences in the environment.
Few studies have considered the effects of bioenergy crops on biodiversity. Bioenergy crops can be broadly categorized as “high intensity, low diversity” (HILD, corn and soybean) or “low intensity, high diversity (LIHD, hay fields and prairies). HILD crops are characterized by high fertilizer and pesticide inputs and are generally annually replanted. LIHD require fewer inputs, are more perennial, and are composed of a mix of several different plant species.
The number of plant species in a field can influence the number of species on a landscape. In general, HILD crops are expected to support fewer species than LIHD crops. The number of bird species is often considered to be a good indicator of the number of animal species in a community. An active group of professional and amateur bird watchers involved with the North American Breeding Bird Survey have produced useful data on the number of bird species in landscapes across North America. Using this data, Meehan et al. developed a model to predict the number of bird species in different future land-use scenarios. Specifically, they contrasted two extremes scenarios for bioenergy crops on marginal lands in the Upper Midwest: (1) changing 9.5 million ha of LIHD into HILD and (2) changing 8.3 million ha of HILD into LIHD. These two scenarios represent opposite ends of the spectrum, moving to mostly perennial (LIHD) or mostly annual (HILD) bioenergy crops on marginal lands.
Their model predicted that changing to a more perennial landscape (hay fields and prairies that are not re-planted every year) would result in more species of birds (up to 200% more) in the landscape while a more annual landscape (corn and soybeans fields) would result in fewer species of birds (up to 65% fewer) in the landscape. This is especially the case for rare grassland birds of particular conservation interest. Which crops are used for producing bioenergy will have consequences for many aspects of the environment, including the number of bird species. It is important to consider all of the costs and benefits of our energy policies.
We all have an intuitive understanding that organisms interact with one another, through such events as predation, parasitism, and even mutualism. It is easy for us to relate to plants and animals this way because we too are often focused on direct interactions between ourselves and the people and things around us. Less often do we consider how we are indirectly linked to one another; that is, how two things influence each other through a shared intermediary.
Field ecologists are often interested in multiple species that are connected to one another through a third living thing, including some in the Gratton Lab at theUniversityofWisconsin-Madison. Steve Hong and his colleagues have been studying how two pests of the important crop soybean affect the plant and one another. Soybean has historically fallen victim to tiny worms called nematodes that attack the plant below the surface. Above ground the plant is fed upon by tiny insects known as aphids which have been introduced to Wisconsin only in the last decade.
Experiments in the laboratory and the field with soybean and its above and below-ground pests have revealed the complicated relationships among them. Winged aphids have been shown to prefer soybeans that are uninfected by the nematodes, both in the lab and in the field. However aphid growth and reproduction were not reduced on plants infected by nematodes versus those that were not infected. However yield and seed production were reduced in the field by nematodes and aphids respectively.
Hong, SC, A MacGuidwin, C Gratton. In review. Soybean aphid (Aphis glycines Matsumura) and soybean cyst nematode (Heterodera glycines Ichinohe) interactions in the field and effects on soybean yield.