What happens to ecosystems when you restore iconic top predators? It’s more complicated than you might think. – UC Santa Cruz – News

Report on the Ecological Impact of Large Carnivore Restoration in North America and its Alignment with Sustainable Development Goals

Executive Summary

A comprehensive analysis of over 170 scientific studies reveals the complex ecological role of recovering large carnivore populations in North America. While restoration efforts are crucial for advancing Sustainable Development Goal 15 (Life on Land), the anticipated ecosystem-wide benefits, such as trophic cascades, are moderated by significant human impacts and environmental factors. This report synthesizes the findings, highlighting the conditions necessary for successful ecosystem recovery and emphasizing that preventing biodiversity loss is a more effective strategy than subsequent restoration. The research underscores the interconnectedness of SDG 15 with other goals, including SDG 13 (Climate Action) and SDG 11 (Sustainable Cities and Communities).

1.0 Large Carnivore Recovery and Its Contribution to SDG 15: Life on Land

The recovery of species such as gray wolves, bears, and mountain lions over the past 50 years represents a significant conservation success, directly contributing to the objectives of SDG 15. The restoration of these apex predators is fundamental to rebuilding ecosystem integrity and halting biodiversity loss.

1.1 Trophic Cascades as a Mechanism for Ecosystem Restoration

The reintroduction of predators can initiate trophic cascades, a process where impacts on prey populations ripple through the food web, leading to broader ecosystem restoration. This mechanism is critical for achieving specific targets within SDG 15.

• Target 15.1: Conservation and Restoration of Terrestrial Ecosystems: The famous example from Yellowstone National Park suggested that wolf reintroduction led to forest recovery by altering elk browsing behavior, thereby restoring plant communities.
• Target 15.5: Halt Biodiversity Loss: By controlling herbivore populations, large carnivores can create conditions that allow diverse plant and animal species to thrive, directly combating biodiversity decline.

2.0 Challenges and Complexities in Linking Predator Restoration to Ecosystem Health

Recent scientific synthesis, led by UC Santa Cruz Professor Chris Wilmers, indicates that the connection between carnivore restoration and ecosystem recovery is often oversimplified. Achieving the desired outcomes for SDG 15 is complicated by a variety of overriding factors.

2.1 Dominant Influence of Anthropogenic and Environmental Factors

The analysis demonstrates that human activities and environmental conditions often have a greater impact on ecosystems than predation alone.

• Human Impacts (SDG 11 & 15): Land-use changes and hunting exert more significant control over the population size and distribution of prey animals like deer and elk than large carnivores do.
• Environmental Constraints (SDG 13): Habitat quality, food availability, and climate-related factors like drought are primary limiting forces on prey populations, often masking the effects of predation.

3.0 Identifying Conditions for Effective Ecosystem Management

The research identifies specific circumstances under which the reintroduction of large carnivores is most likely to produce significant ecological benefits and advance SDG 15.

3.1 Key Conditions for Predator-Driven Trophic Cascades

1. Spatially Constrained Systems: Predators have a greater impact in isolated environments, such as islands, where prey cannot easily emigrate.
2. Multi-Predator Dynamics: The presence of multiple predator species targeting the same prey at different life stages can effectively limit prey populations.
3. Mesopredator Suppression: Large carnivores suppress populations of smaller carnivores (e.g., coyotes) by an average of 18%, which can benefit other species like pronghorns and red foxes, thus enhancing overall biodiversity.

4.0 Broader Implications for the 2030 Agenda for Sustainable Development

The long-term consequences of predator removal and the challenges of restoration highlight the deep interconnections between biodiversity and broader sustainable development objectives.

4.1 Long-Term Ecosystem Degradation

• Impact on Freshwater Ecosystems (SDG 15): In Yellowstone, the historical absence of wolves and beavers altered the park’s hydrology, leading to narrower rivers and reduced habitat for key tree species. This demonstrates that ecosystem degradation can be profound and difficult to reverse.
• Masking Effects of Other Species: The presence of species less vulnerable to predation, such as bison, can continue to exert pressure on plant communities, dampening the restorative effects of a trophic cascade.

4.2 The Importance of Proactive Conservation

The primary lesson from this body of research is the critical importance of preventing species loss. The complexity and extended timeline (50-100 years or more) required to restore the ecological functions of large carnivores underscore the value of proactive conservation.

• Achieving SDG 15.5: Protecting threatened species before they are lost is the most effective and efficient strategy for maintaining ecosystem function and biodiversity.
• Building Resilient Ecosystems (SDG 13): Healthy, complex ecosystems with intact predator populations are more resilient to climate change and other disturbances, contributing to global climate action goals.

5.0 Conclusion and Recommendations

Restoring large carnivore populations is a valuable and necessary component of efforts to achieve SDG 15. However, it is not a simple solution for ecosystem degradation. For conservation and wildlife management to effectively contribute to the 2030 Agenda, the following points must be considered:

• Prioritize Prevention: The most critical strategy is to prevent the loss of large carnivores from ecosystems in the first place.
• Adopt a Holistic View: Restoration initiatives must account for the complex web of human impacts, environmental conditions, and multi-species interactions.
• Leverage Technology: Advanced tools such as GPS telemetry, genetic sampling, and camera traps should be employed to better understand and predict the impacts of restoration efforts.
• Recognize Long-Term Commitment: Policymakers and conservationists must understand that restoring ecological function is a multi-generational endeavor that contributes to biodiversity, ecosystem resilience, and the overall goals of sustainable development.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 15: Life on Land

  This is the primary SDG addressed in the article. The text focuses extensively on the protection, restoration, and sustainable management of terrestrial ecosystems. It discusses the reintroduction and recovery of large carnivores (wolves, bears, mountain lions), their role in ecosystem balance (trophic cascades), the importance of biodiversity, and the impacts of human activities on wildlife and habitats. The article’s core theme revolves around understanding and restoring the ecological functions of these species, which is central to SDG 15’s goal of halting biodiversity loss and restoring terrestrial ecosystems.

2. What specific targets under those SDGs can be identified based on the article’s content?

• SDG 15: Life on Land

  1. Target 15.1: By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests, wetlands, mountains and drylands.

     The article directly addresses this target by discussing the restoration of large carnivores as a means to trigger “ecologically beneficial ‘trophic cascades'” and help “forests recover.” The example of Yellowstone National Park, where the reintroduction of wolves was studied for its effects on the broader ecosystem, including river hydrology and tree species, is a clear illustration of efforts to restore a terrestrial ecosystem.

  2. Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species.

     This target is central to the article’s narrative. It highlights the “remarkable comeback” of species like mountain lions, bears, and gray wolves that were “once nearly exterminated.” This recovery was achieved through protective measures such as the “Endangered Species Act, hunting limits, and reintroduction programs,” which are direct actions aimed at preventing the extinction of threatened species and halting biodiversity loss.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

• Indicators for Target 15.1 (Ecosystem Restoration)

  • Changes in prey animal behavior and populations: The article discusses how the restoration of carnivores can “balance ecosystems by keeping prey populations under control.” The study of elk behavior in Yellowstone, specifically their avoidance of certain habitats and the subsequent impact on tree saplings, serves as an implied indicator of ecosystem function returning.
  • Vegetation and forest recovery: The potential for forests to recover due to reduced browsing pressure from herbivores like elk is a key indicator discussed. The article mentions how “browsing and grazing is suppressing plant growth,” and predators can have an “indirect positive effect on plants.”
  • Hydrological changes: The article implies that ecosystem health can be measured by its physical characteristics. It notes that the loss of wolves and beavers in Yellowstone “changed the park’s hydrology so much that rivers became narrower over time with steeper banks,” indicating that a reversal of this trend could be a measure of successful restoration.

• Indicators for Target 15.5 (Protecting Threatened Species)

  • Population recovery of threatened species: The article explicitly states that mountain lions, bears, and gray wolves have made a “remarkable comeback over the last 50 years” and are “recovering their populations.” This is a direct indicator of progress in preventing extinction.
  • Expansion of species’ range: A specific quantitative indicator is provided for grizzly bears, which “have recovered approximately 100,000 square kilometers of their former range across North America.” This measures the success of conservation efforts in restoring species to their historical habitats.
  • Impact on other carnivore populations: The article provides a statistical indicator of ecosystem rebalancing, stating that large predators “suppress populations of smaller carnivores across North America by about 18% on average.” This demonstrates a measurable effect of restoring biodiversity at the top of the food chain.

4. Table of SDGs, Targets, and Indicators

Source: news.ucsc.edu