Houston ChandlerViews:
We recently had a paper published in the Journal of Herpetology titled Ten Principles from Evolutionary Ecology for the Effective Conservation of Reptiles and Amphibians. Led by Dr. George Brooks (along with other collaborators from Virginia Tech), this manuscript draws from our knowledge about the evolution and ecology of reptiles and amphibians to present guiding principles for their conservation.
While often grouped together, reptiles and amphibians collectively contain a staggering amount of diversity, both at a species level and ecologically. Across these two groups, there are numerous life history traits, strategies, and behaviors that species use to complete their life cycles in almost every ecosystem across the world. It can be challenging for managers tasked with conserving reptiles and amphibians to make informed decisions for a variety of reasons. These challenges include the overall ecological diversity within these groups, complex life histories that rely on both aquatic and terrestrial environments, and a fundamental lack of natural history information for many species. Thus, there is a need for guiding conservation principles that are based on our understanding of the evolutionary ecology of herpetofauna.
The need for this type of work is even more apparent when considering that these groups are disproportionately threatened among vertebrates and yet lag behind other vertebrates with regard to ecological studies and conservation plans. In this paper, we described 10 key principles that we feel can be used to create rules of thumb for reptile and amphibian conservation. This work is designed to facilitate conservation and management of imperiled herpetofauna by providing managers a framework to proactively mitigate extinction risk. Below, I highlight the 10 principles that we feel broadly apply to herpetofaunal conservation. Also included are photographs of some of the incredible diversity housed within reptiles and amphibians.
1. Species declines and recoveries are shaped by abiotic conditions and dispersal capabilities
Ectotherms (species that get their energy from the external environment) are strongly influenced by the surrounding environment, especially temperature and precipitation patterns. These environmental factors ultimately constrain the geographic distribution of many species, and influence how species respond to a variety of global changes. Such changes can ultimately affect population viability and have caused declines and extinctions across a large number of reptile and amphibian taxa. Dispersal capabilities also play an important role in the biogeography of reptiles and amphibians, and their ability to respond to change. Importantly, we lack a detailed understanding of many species’ dispersal abilities, often basing assessments of these factors on expert opinions or related taxa. To make effective conservation decisions, managers must understand species’ fundamental niche (the environment they need to survive and reproduce) and dispersal abilities. For reptiles and amphibians, this will often require designing new studies to fill in critical data gaps in our understanding of relatively basic ecological processes.
2. Habitat, not competition for food, limits local population density
Another important implication of an ectothermic life history is that competition for food is less likely to be limiting in reptile and amphibian populations when compared to endotherms (mammals and birds). Instead, herpetofauna are typically limited in one or multiple ways by habitat features that are linked to the thermal constraints of ectothermy. In practice, these habitat features are variable but can include basking sites, gestation or nesting sites, overwintering sites, anti-predator refugia, or other features that help reptiles and amphibians to regulate body temperature (or moisture). Reliance on such habitat features can lead to patchy distributions across a broader landscape. On the other hand, in areas with plentiful habitat, population sizes or biomass can be very high. For conservation to be successful, practitioners must understand the habitat factors that limit population size across the entire life cycle of a species so that appropriate management actions can be implemented.
3. All environments are stochastic
One of the constant considerations across most if not all environments is that stochastic (random) events have large impacts on species and populations. Many species have evolved strategies that distribute risk in an attempt to manage the uncertainty in natural systems. Increased stochasticity typically leads to higher likelihoods of extinction over many years. However, one of the predominant impacts of global change has been increased variability in species vital rates (growth, survival, reproduction) as a result of multiple stressors from human activities. Given increased stochasticity, resource managers should work to keep species as common as possible to reduce the chances that stochastic processes ultimately lead to extinction events.
4. Successful reintroductions require confronting ultimate causes of decline
Reintroductions, translocations, and other types of population augmentations have become widespread conservation techniques in recent years. However, these types of projects commonly fail to produce meaningful benefits to imperiled species. The primary reason for these failures is a lack of adequate steps taken to address the primary causes of the initial population declines. Too often expensive and challenging reintroduction projects are initiated without a detailed understanding of the environment in which animals will be released. Furthermore, it can take long time periods to understand the population demography of released animals, and success (or failure) can be challenging to document. Released animals must be monitored in sufficient detail to understand their ecology in the new environment or informed management decisions cannot be made. These types of projects are complex and should be implemented using an adaptive management approach that allows managers to meet and adapt to multiple biological and logistical challenges.
5. Vulnerability to threats is a function of innate sensitivity, exposure, and adaptive capacity
One of the fundamental aspects of species conservation is assessing vulnerability to various threats. Such assessments are carried out under a variety of frameworks (e.g., International Union for Conservation of Nature, Endangered Species Act) but typically examine a species’ exposure and sensitivity to particular threats. Recently, assessments have also considered adaptive capacity or the ability of a species to adapt to a changing environment. Making meaningful inferences for reptile and amphibian species can be challenging because of a lack of available data, complex interactions of multiple threats, and a high diversity of life history traits across groups. Precautionary approaches to conservation alongside fundamental ecological research may offer the best techniques to combat these challenges and prevent the loss of reptile and amphibian species.
6. Populations are regulated by negative density-dependence unless they are invading or going extinct
Density-dependent factors are those where the number of organisms (density) directly influences the magnitude of the effect. For example, in a very general sense, populations typically grow at low densities when resources are plentiful but decline at high densities when resources are scarce and competition is high. Such processes can cause natural populations to fluctuate around some equilibrium population size. When populations are rapidly increasing (e.g., invasive species) or declining towards extinction, they are outside of this normal state and normal regulating mechanisms are reduced or absent. Thus, management of declining species typically seeks to return populations to some stable state. For this to be successful, managers must understand how density-dependent factors influence the population in question so that actions can target life stages most likely to influence population growth. Such density-dependent processes can also impact how threats impact populations. Combining an assessment of threats with a detailed understanding of a species’ life history is critical for accurately determining extinction risk and guiding management actions.
7. Fecundity is not always a reliable metric of recovery potential
Across the diversity of herpetofauna, many species produce large clutch sizes in the 100s or even 1000s. In such species, juvenile survival is typically low but can be higher during years with good environmental conditions. High reproductive output can be interpreted as an indication that a species has a high potential to increase in population size (recover from declines). However, this is not necessarily the case as population sizes can be limited by other factors (e.g., loss of habitat). Accounting solely for reproductive output does not predict sensitivity of species to increases in mortality. Ultimately, managers must identify the life stages and/or environmental factors that are limiting population growth.
8. Behavior influences speed of recovery
Behavior is a fundamental aspect of a species’ life history but can be challenging to incorporate into status assessments for imperiled species. A wide variety of behaviors can influence population-level processes, including predator avoidance, foraging activity, habitat selection, or parental care. Such behaviors can impact a species’ ability to respond to stressors and recover from declines. Furthermore, some behaviors may not be evolutionarily advantageous in today’s changing world and can actively contribute to declines. Understanding behavior may be especially important for projects that release animals into novel (for the individual) environments during reintroductions. Overall, amphibians and reptiles can display complex behaviors, including advanced cognition and learning, and accounting for behavior will make conservation and management programs more likely to succeed.
9. Long lifespans evolve when adult mortality is predictably low
Life history strategies exist on a spectrum from r-selected (high reproductive output and low energy input into each offspring) to k-selected (low reproductive output but significant investment into each offspring). Some ectotherms (especially amphibians) have life histories that combine traits from both strategies – high reproductive output repeatedly over many years. These strategies appear to be an adaptation to environmental uncertainty where juvenile survival can be extremely low across multiple years. For such species, additional adult mortality can often have severe negative impacts on long-term population persistence. Long-lived species are also at risk of falling into extinction debt, where reproductive output is unsustainably low but adults are still present on the landscape. This can give the appearance of stable populations when the situation is dire. Long-lived species are also challenging to effectively manage as it can take many years to accurately assess a population’s status and determining the effectiveness (or lack thereof) of management actions can be equally time consuming.
10. Efficient use of resources requires a holistic approach to management
As the previous sections have indicated, there are many things to consider when examining life histories as they relate to conservation. A species’ entire life history is important, but limited resources means that management programs must pick and choose which portions of a life history to focus on. Management programs should strive to ensure that unmanaged portions of the life cycle are not contributing negatively to ongoing conservation actions. For many species, this may mean that additional research is needed alongside active conservation. Ultimately, successful conservation will require a multitude of strategies that target a variety of threats and life history stages.
Overall, there are many challenges facing the successful conservation of reptiles and amphibians. Anthropogenic activities are impacting these groups in many ways, and large numbers of species have already experienced severe declines, range contracts, or even extinction events. The above principles can serve as a guide to help identify species in need of conservation and help identify important considerations for management actions. Management and conservation must ultimately support populations that are resilient to habitat loss, rapid climate change, disease, introduced species, and more.
A PDF of the full publication is available here.
