Wetlands are extremely important ecosystems – they are defined as land areas that are either permanently or seasonally saturated with water, and cover approximately 3% of the Earth’s surface. Despite their small coverage, they store about a third of the world’s carbon and have great biodiversity, but their presence is dependent on climatic and weather conditions.
They support a wide range of species and provide a wide range of services to our population. Thousands of resident bird species use wetlands as feeding and breeding grounds and many more use them as a stop off during migration. Wetlands, therefore, support a diverse range of species and contain many vital habitats.
Connectivity among these habitats is essential, as it enables passage for various animals. Wetland areas are vulnerable to human activity, and are often located in areas where such activity is prominent (e.g. ports, farmland, industrial areas, etc.). Human activities often lead to the destruction of wetlands and changing land covers that can affect connectivity, adding barriers to movement, and limiting network connections among wetlands. Ultimately animal habitats are destroyed, as well as their ability to move between them. This could consequently reduce the numbers of ecologically favourable settings for breeding or feeding, seriously impacting animal populations.
Dr Franklin Schwartz and his colleagues are currently studying how certain groups of animals move between patches of wetland habitat in order to understand how this is affected by human activities and how connectivity could be affected by future changes.
The northern part of the Great Plains region of North America is sprinkled with “prairie potholes” – shallow indentations on the ground surface that form pools and lakes when filled with water, mostly through snowmelt or rainfall. These potholes act as a brooding ground for many migratory waterfowl, such as ducks, in the Spring and Summer months. These small water bodies promote the growth of freshwater plants that act as a source of food, and enable ducks to safely rear their young before migrating south when the temperature drops.
Prairie potholes play a vital role in the life cycles of these ducks, so the extent of their presence directly affects the size of the population each year. Their presence here is dependent on weather conditions: in years when there is little rainfall, fewer pools are likely to form so the region can only support a smaller migratory bird population. These populations could therefore be vulnerable to climate change and other factors, such as changes in land use, that might affect the sustainability of these wetlands.
Grasslands in the Great Plains area are currently undergoing conversion into farmland, which means that the extent of grasslands surrounding prairie potholes is reduced. It has been found that some species prefer to settle in ponds that are surrounded by a large area of grassland, and the grasslands act as pathways between wetlands for species to move along. The reduction of their extent limits the ability of animals to move between these waterbodies and reach important habitat areas.
Connectivity between different habitats and patches within the same habitat is a critical factor affecting animal populations. Habitats are becoming more and more fragmented, as pressures, like urbanisation or crop production and related environmental changes, cause habitats to be destroyed. Connectivity among these fragments or patches is essential for species to disperse. So, for example, two different woodlands could be connected by a stream with riparian (wetland) vegetation along its banks, or two different patches of woodland within a field could be connected by a hedgerow.
In the case of the Prairie Pothole Region, waterbodies are connected by grasslands, which facilitate the travel of amphibians and other animals among them and protect nesting birds from predators. Native grasslands in this region were developed under a dry climate, on rocky, clayey soils, which are marginal for farmland. Now land is increasingly being converted for corn and soybean cultivation. This then leads to the destruction of pothole water bodies, leading to disconnections between remaining potholes, ultimately reducing the availability of these vital ecological refuges and the ability of species to move among them.
Climate change is a source of pressure on many ecosystems and ecological processes. The presence of prairie pothole wetlands is affected by the weather and the climate, and these potholes act as important nesting areas for many bird species, as well as small mammals and amphibians. The extent of the effect of climate change on these areas and the species that depend on them is currently unclear, as different species have different levels of dependence on these wetlands, and the hydrological processes and behaviour of these lakes are also poorly understood. As such, it would be difficult to try and determine how they would respond to climate change.
This is where the work of Dr Ganming Liu, Dr Nancy McIntyre, Dr Frank Schwartz and Dr Christopher Wright comes in. Their current collaborative study aims to understand the hydrological processes behind the prairie wetlands and how they respond to the current climate before modelling how they might respond to future changes in climate. They then hope to use this knowledge to further understand how waterfowl and amphibians disperse and move between wetlands, as well as determining how land use and climatic changes will affect this, identifying barriers to connectivity and establishing which habitats are less likely to be affected by environmental change. Their research involves mapping potholes and then visualising a network by connecting pools that are within a certain proximity to one another, which displays how these wetlands are connected through time. Connectivity varies for different groups of animals, depending on how far they can travel. If wetlands are still well-connected under the future climate for waterfowl, this may not be the case for amphibians, so this research is key for understanding how these different groups will be affected by climate change – identifying which areas would need a greater conservation effort.
The continuing conversion of grassland to corn and soybeans impacts both wetland waterbodies and surrounding habitat. Smaller waterbodies are simply ploughed and farmed during drier years, which destroys their functional value as wetlands. Land-cover conversions from grassland to farmland also negatively impacts nesting success for ducks. Predicted increases in temperature and somewhat wetter conditions will promote the continuing loss of grasslands to corn and soy crops.
What strategies could be followed to protect these habitats if changes in land use and the climate have a detrimental effect on them?
US government programs e.g., Conservation Reserve Program (CRP), have been in place since 1985 to pay farmers to retire land from farming. This program has helped to protect wildlife habitat. However, the high commodity prices for corn and soybeans, wetter weather and subsidised crop insurance have promoted a modern expansion in farming. Thus, grasslands are actively being converted to corn and soybean production and lands are being removed from the CRP. There are few reasons to be optimistic for strategies to affect a turnaround.
What makes the Prairie Pothole Region an ideal area for migratory birds?
The Prairie Pothole Region is unique in the world because its large size, nearly three quarters of a million square kilometres, incorporates several million wetlands ponds and lakes within grassland and agricultural settings. These waterbodies are very productive for birds due to their relatively shallow and constantly changing water depths. These features facilitate nutrient cycling and a variety of aquatic plants and animals. Termed America’s “duck factory”, the Prairie Pothole Region is the most productive waterfowl habitat on the continent, perhaps even the world. It also supports shorebirds, grassland birds and other wildlife.
Of waterfowl and amphibians, which do you think is more vulnerable to changes in connectivity?
Amphibians are examples of animals that disperse over land. Unlike birds, they can’t fly to find new habitats. So, they will be more sensitive to changes in connectivity, particularly those stemming from land use changes. Even during the breeding season, when most ducks are effectively tied down, waterfowl are able to interact with landscape at a larger scale than do amphibians, meaning that they potentially have more options.
Is climate change or human land use more likely to affect prairie pothole connectivity?
Land use conversion represents the greatest impact to prairie pothole connectivity. Smaller wetlands tend to disappear in the crop fields and nests in larger wetlands are more prone to predation with the loss of nearby grasslands. Climate change is expected to be a contributing factor no matter what climate ultimately emerges. Hotter and drier will reduce the wetland habitat as the numbers of pothole wetland decline from evaporation. Hotter and wetter appears to improve the prospects for farming but reducing waterfowl production.
The research team studies climatic and anthropogenic forces affecting the wetland systems of America’s Great Plains. At stake is the future of migratory birds and other animals that depend critically on the millions of water bodies dotting the plains.
This study was supported in the United States by National Science Foundation (NSF) awards 1340548, 1340648, and 1544083 (MacroSystems Biology Program).
Other members of our research collective at South Dakota State University, Kansas State University, University of Minnesota Duluth, and the United States Geological Survey.
Team members have expertise in ecology, complex systems, and hydrology. Franklin Schwartz at Ohio State University has interests in water, society and health. Ganming Liu is an assistant professor at Bowling Green State University with interests in modelling complex hydrologic systems. Professor Nancy McIntyre at Texas Tech University works at the intersection of community ecology, landscape ecology, and conservation. Chris Wright is a landscape ecologist and complex system analyst at the Natural Resources Research Institute, University of Minnesota Duluth.
Dr Franklin W Schwartz
The Ohio State University
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