Snow geese are considered a keystone species in their Arctic breeding grounds. Keystone species are organisms that have an outsized influence on their environment and play a critical role in maintaining the structure of their ecosystem. There are a few reasons why snow geese are considered a keystone species:
Snow geese maintain the tundra habitat
Snow geese rely on the open tundra habitat in the Arctic to breed and raise their young. As the geese walk across the tundra, their feet till and disturb the soil, preventing trees and shrubs from taking over the landscape. Their grubbing also helps fertilize the soil. This creates ideal conditions for low-growing tundra plants and wildflowers to grow each spring and summer. These plants provide essential food and nesting resources for many other animals that inhabit the tundra.
Snow geese transport nutrients
Snow geese transport nutrients between their Arctic breeding grounds and wintering areas further south. In the spring, the geese fly north and deposit nitrogen-rich waste onto the tundra from their winter diets. This influx of nutrients fertilizes the soil and boosts plant growth. In the fall, the geese eat plants on the tundra and then migrate south, transporting some of those nutrients to their wintering grounds.
Snow geese impact vegetation
Through their grubbing and grazing behaviors on the tundra, snow geese greatly impact the vegetation composition. They preferentially feed on certain plant species, reducing competition and allowing other species to become more abundant. The geese also fertilize the soil with their droppings, changing nutrient cycling processes. These impacts change which plants are able to grow and how productive the vegetation community can be as a whole.
Snow geese provide food resources
Snow geese provide a significant seasonal food source for Arctic predators when the geese are breeding on the tundra. Foxes, wolves, bears, and many bird species prey on adult geese, goslings, and eggs during the summer months. This helps sustain predator populations that have limited food availability during the rest of the year when the geese are not present. Declines in snow goose populations could have cascading effects on predator numbers in the Arctic.
Interconnections in the food web
As a dominant herbivore in the Arctic tundra ecosystem, snow geese are intricately connected to many facets of the food web. They directly and indirectly influence the abundance and distribution of hundreds of plant, insect, bird, and mammal species through their grazing, grubbing, nutrient transport, and role as a prey species. Disruptions to snow goose populations can potentially reverberate through much of the Arctic’s fragile food web.
Role in nutrient cycling
By transporting nutrients between the Arctic tundra and their more southerly wintering grounds, snow geese play an important role in nutrient cycling at a continental scale. Nitrogen deposited by the geese in the Arctic boosts plant growth and productivity during the short summer growing season. Phosphorus and other nutrients carried south by the geese can enrich lakes, wetlands, and agricultural areas where the birds spend the winter.
Impacts on vegetation structure
Intense grubbing and grazing by dense snow goose populations can alter the vegetation structure on the tundra. In some cases, overgrazing by geese has converted areas of the Arctic coastal plain from moss/sedge meadows to almost complete bare ground and mudflats. This can hasten coastal erosion and be detrimental to other species that rely on intact tundra vegetation. The geese’s impacts on vegetation structure make them an important management consideration.
Creation of habitat mosaic
The uneven grazing and grubbing pressure exerted by snow geese creates a diverse mosaic of habitats across the tundra. Heavily grazed and grubbed patches are interspersed with intact meadow zones. This habitat heterogeneity benefits many other species in the Arctic that utilize different ecological niches. For example, shorebirds often nest in the mudflats created by the geese, while songbirds favor the intact meadow areas.
Influence on wetland hydrology
On the Hudson Bay lowlands, intensive grubbing and grazing by lesser snow geese has impacted wetland hydrology by disrupting vegetation that ordinarily slows and stores precipitation runoff. Loss of this vegetation has led to increased spring snowmelt flows, raised water tables, saltier soils, expanded wetland area, and overall wetter conditions. These hydrological changes can stress tundra plants and make the habitat less suitable for some nesting waterfowl species.
Cascading effects on food webs
As a numerically dominant herbivore that also serves as prey for numerous predators, snow geese have far-reaching impacts that cascade through Arctic food webs. Declines in goose populations from over-hunting in past centuries caused crashes in predator numbers. Likewise, the exponential growth of snow goose populations in recent decades may be altering predator-prey dynamics, affecting the reproductive success of lemmings, shorebirds, and other tundra species.
Relationships with microbes
Snow geese have complex relationships with soil microbes that underpin the ecology of the Arctic tundra. Goose droppings deposit nitrogen and other nutrients that boost microbial growth. Trampling and grubbing by geese also alters soil aeration, moisture, and temperature in ways that influence microbial communities. In turn, these microbes drive critical nutrient cycling and decomposition processes that impact plant growth and ecosystem productivity.
Seed dispersal
Snow geese provide some dispersal services for seeds and invertebrate eggs as they move between nesting colonies and wintering grounds across a vast geographic range. Viable seeds pass through the geese’s digestive systems and are deposited through feces. Invertebrate egg cases and plant material can also get lodged on the geese’s feet and feathers and transported long distances.
Grazing optimizes plant growth
The grazing pressure exerted by dense snow goose populations during the Arctic summer helps optimize plant growth in some ways. Grazing removes older low-productivity plant tissues and stimulates new growth. It also keeps the tundra vegetation structure low and open, allowing more light penetration to reach lower layers. This grazing optimization is one reason why the artic tundra can support such large populations of geese.
Creation of nesting habitat
Intense grubbing and grazing by snow geese creates ideal nesting conditions for some Arctic bird species. Bare mudflats dotted with small ponds and puddles provide prime habitat for shorebird nests. Snowy owls also often nest in the open barren landscapes caused by goose overgrazing. So while reducing vegetation cover, geese provide specialized nesting opportunities.
Stimulation of greenhouse gas release
Trampling and grubbing of the tundra by dense goose populations releases additional greenhouse gases from Arctic soils and permafrost. The destruction of insulating vegetation exposes more ground to warmer air temperatures, accelerating permafrost melt. Goose activities also directly aerate soils, stimulating microbial respiration and carbon dioxide release. Overall, snow geese may amplify climate change impacts in the Arctic.
Vectors of disease
As migratory species that travel in dense flocks and interact with many other birds, snow geese have the potential to spread diseases between populations and ecosystems. Viruses that geese carry, such as avian influenza, could be disastrous if introduced into new areas. Understanding the role of snow geese as disease vectors between the Arctic and more southern regions is an important area of research.
Effects on water quality
Large amounts of snow goose droppings entering Arctic ponds and lakes can adversely impact water quality. Goose feces contain high levels of nutrients such as nitrogen and phosphorus. This can spur algae blooms and lower dissolved oxygen levels, degrading aquatic habitats for other species. Snow goose presence is linked to increased cyanobacteria populations in High Arctic waterbodies.
Conclusion
In summary, snow geese have a variety of complex and interconnected ecological impacts across the Arctic tundra and boreal forest ecosystems where they live and breed. Their inhabitation behaviors, grazing, grubbing, nutrient transport, and role as prey make them a classic example of a keystone species. Snow geese exert influence disproportionate to their actual biomass and shape the structure and function of Arctic environments in many ways. Their unique niche and far-reaching effects qualify snow geese as important drivers of Arctic ecology and exemplify what it means to be a keystone species.