The Bison in the Living Room: Wildlife Coexistence, Connectivity, Corridors, and Strongholds

As the scientific discipline of ecology grows, new slogans, terms, and subdisciplines are necessarily created because humans must be involved if we are to protect life on Earth (biodiversity). For example, the creation of conservation biology over 30 years ago promoted population genetics, an important aspect that had previously been underemphasized in conservation. Similarly, landscape ecology—‘spatial mapping’ of ecological phenomena on the empirical landscape—turned out to be a landmark step in putting theory into practice. Even today, we see Artificial Intelligence (AI) assisting wildlife conservation by popularizing, further developing, and upgrading what statisticians have been doing with neural networks for decades. Collectively, we are devising new approaches and techniques to work towards protecting our wildlife populations—especially those species in peril. 

This species-level focus is key to sustaining and restoring healthy ecosystems, the basic subdivision of life on Earth. Why is that? The famous biologist E.O. Wilson organized biodiversity into three basic levels: ecosystems, species, and genes, and placed further priority on the species level because it integrates interrelationships with both genes and ecosystems. Species carry genetic information, add structure and function to ecosystems, are easier to understand and study, and provide the main and practical means for humans to manage and restore genetic diversity and ecosystem health—both vital to the all-important concept of ecosystem resilience in a changing world. Human activities are rendering ecosystems unable to rebound after unnatural, sustained impacts. The subsequent irreversible changes in these ecosystems are the biggest alarm call for the conservation of biodiversity. It’s time to take action and focus on solution science that applies and tests new knowledge.

At the confluence of landscape ecology, population genetics, and conservation biology, a variety of related terms arose—connectivity, corridors, crossings, greenways, etc.—that are collectively referred to as wildlife connectivity, or corridor ecology. An excellent treatise on this subdiscipline is Corridor Ecology: Linking Landscapes for Biodiversity Conservation and Climate Adaptation written by colleagues Jodi Hilty et al., 2019. They look at how important landscape features, often linear, can be managed and arranged to allow wildlife to move to and from quality habitat. This is critically important for the recovery of a wildlife population that has substantially declined because human activities have caused massive reduction and fragmentation of their native habitats. Individuals become isolated from natural movement patterns that access vital resources to survive and reproduce. This conflict brought forth the question of how to best design and manage the landscape—both public lands and private working lands—to maintain and restore viable populations that are resilient to impacts from human activities and climate change. This is not easy in a human-dominated landscape delineated with political and jurisdictional boundaries that are largely invisible and often come without warning to susceptible, vulnerable wildlife species.

Before light is shed on the bison in the living room, it’s important to take a step back and look at the basics, because no matter how we use the many approaches to promote a ‘conservation fix,’ we must first understand the root cause of population decline. With this knowledge in hand, then and only then, can we proceed with a successful conservation solution. To that end, wildlife biologists often identify the characteristics of variable-sized habitat patches that reward the wildlife species that exploit the resources within those patches for their survival and reproduction. Evolution selects for wildlife behaviors that exploit these safe, stronghold habitats where species experience nutritional and demographic rewards. However, the risks in these strongholds are often ignored or misunderstood, rendering the analysis, and subsequent understanding, deficient. When such diagnostics models are broadcast in the scientific and popular literature, there is a strong probability that decision-making done with these deficient, uninformative models will be biased and lead to mismanagement.  

Thus, stronghold habitats have been defined as a portion of a source population where a species survives to reproduce and has enough surplus to maintain its numbers and populate surrounding areas, called population sinks. We further define it as a spatial unit where populations are demographically strong, genetically diverse, and the resources they contain have a high intrinsic potential to support a particular species, or suite of species. The concept became popular with conservation efforts aimed at restoring species in peril, like salmon or tigers. Although implicit, YERC’s WildNET program specifically adds demography—survival and reproduction—to this definition: where a species can survive to reproduce and pass its genes to future generations. This adds a vitally important measurement of success or performance metric needed to evaluate, learn from, and adjust the conservation decision-making process in a timely manner at a time of rapid change—from both climate and human impacts. So if we include all known risks and rewards, we can better identify and quantify stronghold habitats by using performance metrics that are good indicators of the ultimate goal: genetic fitness where individuals survive to reproduce and increase their genetic contribution to future generations.

What structurally looks like high-value habitat can be riddled with risks such as disturbance, predation, overharvest, disease, and structures such as fencing and roads. Measuring abundance is vitally important but can also be misleading because individuals, drawn to a particular stronghold and counted, could just be passing through without reproducing. So it becomes vitally important to determine if there is a sufficient amount of habitat or carrying capacity for the population in question to survive and reproduce. For these reasons, YERC’s WildNET program is focused on the quantification of stronghold habitat characteristics with regard to not only it’s carry capacity or habitat value—indicated by the probability of a particular species selecting that stronghold—but also its contribution to a species’ genetic fitness as it attempts to survive and reproduce across all the habitats included in their home ranges. Our past research terms this approach a ‘RRSC’ (pronounced ‘risk’) population model, or a Risk-Reward Spatial Capacity population model. This approach is described in a 2012 book chapter which is a decision-making framework that marries spatially-explicit habitat selection models with temporally-dynamic population models. Finally, if there is not a sufficient amount of stronghold habitat for a particular species’ genetic fitness, then conservation action needs to be taken to allow wildlife species to access additional amounts by linking or connecting strongholds with safe passage (corridors).

We will very likely make mistakes in population management decisions, conservation programs, and restoration programs if we don’t stay focused on the best available scientific methods to account for, and identify, the root cause(s) of mortality—the risks as well as the rewards of strongholds—as well as where and when they occur and the degree they interact. And even if mistakes are made, we can learn and then adjust—adaptive management—if we commit to long-term monitoring that can also provide for cutting-edge science that gets at cause and consequence and leads to accurate, adaptive decision-making. For example, some causes of mortality interact and substitute for another, such as a predator may prey on an ungulate—a fawn in the summer or an older bull elk in late winter—that are nutritionally compromised and likely to die anyway. Yet others are tragically more additive to other forms of mortality—for example, harvesting a healthy pregnant cow elk, or excluding it from valuable winter range forage. We’re flying blind without this basic knowledge of the risks and rewards at critical life history stages—that often occur during the winter—of each species, especially today when the impacts of climate and human activities are interacting in unpredictable ways that are rendering traditional management and decision-making systems ineffective.  

So I submit that the bison—our elephant—in the living room is our too-often ignorance to face the basic empirical facts that a very large majority of catastrophic declines in species populations (and extinctions) worldwide, and in the GYE (Greater Yellowstone Ecosystem), are attributable to two major root causes: (1) overharvest or killing, and (2) major loss of natural, evolved habitat. It’s not rocket science. Again, new terms, slogans, and subdisciplines can add to our understanding of the root causes and consequences, but if we don’t first identify and quantify the casualties of population fluctuations which are tightly linked to available resources in sufficiently connected stronghold habitats, then whatever conservation decision we make will likely be ineffective in recovering and/or sustaining a healthy population. Benchmarks of success are needed, for example, to mitigate the causes of loss head-on by identifying where and when mortality occurs, and, similarly, what habitat and nutrition resources are available to promote reproduction and recruitment of neonates in the adult breeding population. These are often-ignored aspects of successful human-wildlife coexistence strategies. Here, coexistence is defined as a sustained state in which humans and wildlife can co-adapt to living in shared landscapes—stronghold habitats–where human impacts on wildlife are identified and then governed in a way that ensures long-term wildlife population resiliency (genetic fitness), social legitimacy, and tolerable levels of risk.

Benchmarks for success, starting with a verified baseline, suggest the evaluation of different choices and options when attempting to restore or recover a species that has been impacted. This is the fundamental underpinning of the NEPA (National Environmental Policy Act) where the perpetrator must justify its action and lay out mitigating and adaptive options to choose from. It’s also akin to running a successful business: know your current stock and set your performance metrics (measures of success). For wildlife, it’s rather simple: survive in order to successfully reproduce (fitness). This demands that we quantify stronghold habitats. For example, why construct a 5 million dollar overpass if it doesn’t at least increase overall survival and reproductive success of the target population, let alone reduce wildlife-vehicle collisions? Why create landowner incentives to decrease depredations using lethal means when they are not economically and/or socially justified? Are non-lethal means (often referred to as coexistence strategies) more cost-effective? Do they support additional benefits which increase profit margins compared to other land-use activities on adjacent lands (wildlife viewing and hunter harvest)? Finally, how are we evaluating and/or auditing the various alternative choices?

Take bison for example! We know from history that humans nearly killed them off to extinction if it were not for a small group of concerned conservationists that worked together to allow the remaining few in the protected area known as Yellowstone National Park. With a population reduction of over 99%, we catastrophically disrupted the North American continent by functional extinction of the major grazing herbivore in terms of biomass, but also a key process known as migration—a recurring seasonal pattern whereby a species impact forage—is distributed over space and time and greatly lessens the impact to plant communities. These migrations undoubtedly evolved over thousands of years—along with other factors like predation, competition, fire, and climate—to establish a dynamic steady-state condition that shaped the great plains and grasslands of North America.

Bison, like other large mammal species—ungulates and carnivores—that barely survived human killing in the 19th and 20th centuries, are capable of moving many miles during a short period and are beginning to repopulate their former historic ranges. In doing so, they are now facing an insidious form of habitat loss where bison, for example, are denied access to seasonal stronghold habitats. As they attempt to ‘learn’ new migratory routes, they seek modern analogs to their historic grasslands and face continued mortality risks, primarily on their low elevation winter range. This brings up a whole host of questions with regard to root cause and consequence. For example, as we attempt to restore migratory and dispersing large mammal species, how do we know what stronghold habitats to focus on? Are today’s migration, movement, and dispersal routes artifacts of past culturally evolved corridors or are they recent? Are they ephemeral and disappear in a few years due to changing impacts like changing forage production patterns or any one of numerous human activities? Does a study that lasts a few years tell us what habitats and movement corridors are most important to protect in the long-run when so many dynamic factors—that vary seasonally and annually—affect their movements? What about the impacts of migratory species on their forage and prey—trophic cascades—when they are ‘forced’ to stay on their summer range during the winter? Even if we understand the natural seasonal and annual variation in movement and migratory corridors that best support a healthy ecosystem for all species (biodiversity), how can we identify and prioritize the most important stronghold habitats to connect in space and time so that our imperiled large mammal species survive and successfully reproduce but also avoid conflicts with humans (vehicle strikes, depredation on livestock and crops, etc.)?

Take today’s famous stronghold—a potentially safe haven habitat—for many large mammals, called the northern ungulate winter range of Yellowstone National Park (YNP) which includes an area adjacent to YNP called Paradise Valley. This is where species like ungulates—elk, pronghorn, mule deer, and bison—attempt to migrate from protected summer range down to their historic lower elevation winter range, primarily in Paradise Valley. These species, along with dispersing carnivores, seek safe stronghold habitats to survive the energetic bottleneck called winter. With the required nutrition demands of winter comes significant risk to gain the reward of forage and prey. During this winter period, all the mature females of these large mammals are pregnant, which adds to the population risk and can come with great consequences.

While talking with quantitative ecologist and wildlife demographer Dr. Kenneth Wilson of the Fish, Wildlife and Conservation department at Colorado State University (and YERC board member), he mentioned the similarity of wildlife moving to and from lower elevations as “navigating the streets of a major city where a migrating ungulate or dispersing carnivore attempts to safely move forward during a risky ‘green light’ and only stop at a ‘red light’ or supposed safe stronghold.” Similarly, and even more morbose, is the “red light, green light game” during the first episode of a popular TV series called Squid Game. It provided a stark example of the problems an individual faces when leaving their more-or-less protected home in Yellowstone National Park. Individuals are seeking to avoid a ‘debt’ that, for wildlife, is a lack of nutrition during winter. In that show, the slightest misstep or confusing rule ended in death, and few made it to the finish line. Similarly, wildlife often face a juggernaut of additional human risks—a spatially-confusing maze of choices that are difficult to perceive and respond to. These mortality risks are often in addition to natural mortality factors they face during the winter energetic bottleneck where they need to gain enough food to survive, especially for pregnant females.

Clearly, a new approach is needed for wildlife population ecology and management. One that is evidence-based, focused on causality, verifiable, transparent, repeatable, and includes management and conservation decision-making that adjust to annual performance metrics (e.g., 60% survival). Thus, in our WildNET program, we are focused on population models, full of real empirical field data, that are capable of quantifying all landscape factors—both risks and rewards that include different impact scenarios such as land-use, hunting, climate, habitat, forage, prey, and predators. We build these models in a way that end-users can predict the consequences of many different What-if-Scenarios—natural and human-caused impacts—on wildlife populations. An example of this is found in a chapter of the book GeoDesign. We evaluate species of interest by addressing how impacts promote survival or add to mortality, for example, how a particular stronghold affects their genetic fitness, whether connected or not. Remember, population ecology in a nutshell goes like this: you must compete to eat and not get eaten in order to survive and then reproduce. That’s a simplification, but it underscores what real coexistence strategies are about and how the many risks and rewards that species face during their life history stages culminate in passing on their genes or not. So let’s take a razor-sharp focus on how the causal factors (both human and non-human) affect species decline and recovery.

From my young adult years as an avid hunter, angler, and fur-trapper, to my adult career as a conservation ecologist involved in large mammal research and monitoring, I have always advocated for a common sense, evidence-based approach to science that aids in sustained decision-making. In evaluating different alternative choices, I use three yardstick measures, called the three “E’s.” First is Ecology. What does an objective, independent assessment using the best available science say about the issue or impact? Second, Economics. What is a full-cost accounting, including unpriced values, of the proposed action and its impact cost to humans, wildlife, and the ecosystem they inhabit? Finally, what are the Ethical considerations of the impact given alternative choices, including no-action? This is where the ecological and the social sciences—and their open, repeatable, predictive, and transparent methods—can identify the best option(s) that sustains healthy wildlife populations while hopefully providing economic incentives that work for people. This is the basis of a sound coexistence program that is also embedded in our WildNET program, where all stakeholder groups—academia, agencies, NGOs, businesses/corporations, Indigenous Nations, and the general public, especially landowners—work together to collect trusted data that can then be used for sustained decision-making according to the three-E yardstick measures and their performance metrics, so that the options can be adjusted as needed to adapt to change (climate, market trends, land-use, etc.). 

We seek the truth—from common sense to experiments—that’s out there in nature. This ‘science’ needs to avoid the politics of mis- and dis-information campaigns, all too common among, within, and between stakeholder groups. After all, empirical evidence is the key to finding the truth as well as gaining the trust of landowners, whether it’s ecological, judicial, or forensic. Such scientific information that adds reliable knowledge can come from landowners, biologists, managers, and businesses—not just from academia. So let’s look directly at the bison standing in the living room, waiting to move forward and start with the root causes of population fluctuations. What is the consequence of the trophic and societal impact (called a crime in judicial systems)? How can we remedy and prescribe—called restorative justice? Where is the evidence? Are the methods used to gain evidence both transparent and repeatable? In the environmental, ecological, and social sciences, we similarly look at the consequential impacts of the human perpetrator which is what we attempt to do with county, state, and federal statutes like the NEPA on species populations and attempt to mitigate and adapt. We weigh all the evidence and make decisions. That’s why we’re excited to apply our WildNET principles and approaches to restoring species populations so we can all coexist sustainably in our home ecosystems across generations.