Animal Population Trends Research Articles

Navigating the bioacoustic landscape: Standardization and interoperability of acoustic data products

The importance of bioacoustics for understanding and protecting the natural world has grown significantly over the last few decades. Our capacity to monitor the acoustical landscape has increased with lower cost instrumentation, improved communication, infrastructure, and storage, as well as the development of reliable machine learning methods for analysis. Understanding long-term trends in animal populations as well as the impacts of anthropogenic noise requires the ability to retain and interpret records over decadal time scales, record in detail what type of analysis has been performed and understand when multiple analyses may be combined and when they should not be. This is not possible without a well-defined set of terms and meanings. In this talk, we will provide an overview of the work of Acoustical Society of America’s working group S3-SC1-WG7 that has been charged with developing an American National Standards Institute standard for bioacoustics information derived from acoustic recordings. The proposed standard details what information should be recorded for bioacoustics recording and analysis effort, ranging from specification of data to be noted about instrumentation to information gleaned from recordings such as noise levels, animal calls, and acoustic source locations.

Duration and variability of spring green-up mediate population consequences of climate change.

Single phenological measures, like the average rate of phenological advancement, may be insufficient to explain how climate change is driving trends in animal populations. Here, we develop a multifactorial concept of spring phenology-including the onset of spring, spring duration, interannual variability, and their temporal changes-as a driver for population dynamics of migratory terrestrial species in seasonal environments. Using this conceptual model, we found that effects of advancing spring phenology on animal populations may be buffered or amplified depending on the duration and interannual variability of spring green-up, and those effects are modified by evolutionary and plastic adaptations of species. Furthermore, we compared our modelling results with empirical data on normalized difference vegetation index-based spring green-up phenology and population trends of 106 European landbird finding similar associations. We conclude how phenological changes are expected to affect migratory bird populations across Europe and identify regions that are particularly prone to suffer population declines.

Co-management brings hope for effective biodiversity conservation and socio-economic development in Vwaza Marsh Wildlife Reserve in Malawi

Co-management has been widely promoted in protected area management on the premise that it may simultaneously enhance biodiversity conservation outcomes and improve livelihoods of the park-border communities. However, the success of this management approach remains a growing debate raising the question of its effectiveness. To contribute to this debate, we used local community perceptions and secondary ecological data to assess the extent to which co-management has effectively contributed to biodiversity conservation and socio-economic development outcomes in the Vwaza Marsh Wildlife Reserve. Face-to-face individual interviews using a semi-structured questionnaire were used to collect data on the perceptions of co-management from 160 purposively selected heads of households. A desk study was used to collect data on trends in animal populations, animal mortality, and prohibited activities including incidences of poaching for the past 30 years (pre-and post-introduction of co-management). Results showed that local communities have positive perceptions of the conservation work in the Vwaza Marsh Wildlife Reserve. Further, there was an improved people-park relationship and a recovery of animal populations in the reserve after the introduction of co-management. These findings point to the success of co-management in the area. However, misunderstandings over revenue sharing were still a thorny issue, somehow creating mistrust between parties. We concluded that while it may still be early to achieve more demonstrable conservation outcomes, co-management appears to bring hope for effective biodiversity conservation and socio-economic development in the Vwaza Marsh Wildlife Reserve. Participatory evaluation of co-management involving key stakeholders is recommended in the Vwaza Marsh Wildlife Reserve based on the findings of this study and lessons learnt over the years.

Designing a large-scale track-based monitoring program to detect changes in species distributions in arid Australia.

Monitoring trends in animal populations in arid regions is challenging due to remoteness and low population densities. However, detecting species' tracks or signs is an effective survey technique for monitoring population trends across large spatial and temporal scales. In this study, we developed a simulation framework to evaluate the performance of alternative track-based monitoring designs at detecting change in species distributions in arid Australia. We collated presence-absence records from 550 2-ha track-based plots for 11 vertebrates over 13years and fitted ensemble species distribution models to predict occupancy in 2018. We simulated plausible changes in species' distributions over the next 15years and, with estimates of detectability, simulated monitoring to evaluate the statistical power of three alternative monitoring scenarios: (1) where surveys were restricted to existing 2-ha plots, (2) where surveys were optimized to target all species equally, and (3) where surveys were optimized to target two species of conservation concern. Across all monitoring designs and scenarios, we found that power was higher when detecting increasing occupancy trends compared to decreasing trends owing to the relatively low levels of initial occupancy. Our results suggest that surveying 200 of the existing plots annually (with a small subset resurveyed twice within a year) will have at least an 80% chance of detecting 30% declines in occupancy for four of the five invasive species modeled and one of the six native species. This increased to 10 of the 11 species assuming larger (50%) declines. When plots were positioned to target all species equally, power improved slightly for most compared to the existing survey network. When plots were positioned to target two species of conservation concern (crest-tailed mulgara and dusky hopping mouse), power to detect 30% declines increased by 29% and 31% for these species, respectively, at the cost of reduced power for the remaining species. The effect of varying survey frequency depended on its trade-off with the number of sites sampled and requires further consideration. Nonetheless, our research suggests that track-based surveying is an effective and logistically feasible approach to monitoring broad-scale occupancy trends in desert species with both widespread and restricted distributions.

Stakeholders engagement as an important step for the long‐term monitoring of wild ungulate populations

Abstract Monitoring trends in animal populations is essential for the development of appropriate wildlife management strategies. However, long‐term studies are difficult to maintain mainly due to the lack of continuous funding. In this scenario, the collaboration between local stakeholders and researchers can be a fruitful partnership to monitor game species for long periods and vast territories. We present an experimental framework with the involvement of researchers, local hunters and game managers for the continuous monitoring of wild ungulate populations. By combining vehicle‐based counts with distance sampling techniques, we implemented and validated a sampling scheme able to provide demographic information for the effective management of wild ungulate populations. Here, we used an Iberian red deer (Cervus elaphus) population as a model. The project implementation involved 30 participants including 24 stakeholders and 6 field technicians/data analysts with experience in monitoring wild ungulates. A total of eight teams covered 29 itineraries, synchronously, in two periods of ecological relevance for red deer, early summer and early autumn. Density estimates were consistent among sampling periods and characterized by acceptable coefficients of variation (approximately 20%). Our results prove that the application of the proposed framework is feasible (three to four itineraries per team), cost‐ and time‐effective (one week per sampling period) and produce population estimates fit for management. Being based on direct observations, the method would provide important demographic indicators (e.g. population density, age structure and fawn recruitment, and group size) about wild ungulate populations. Apart from engaging interested stakeholders, the success of our proposal relies on three key actions including the theoretical and field instruction of participants, the definition of timely and unbiased survey designs and the maintenance of participants’ motivation. The implementation of rigorous and standardized sampling protocols is pivotal for data integration through time and space. In the absence of continuous funding, the voluntary collaboration between entities should be fostered to study and mitigate the potential threats to wild ungulate populations resulting from disease, unregulated hunting and environmental changes.

Management resourcing and government transparency are key drivers of biodiversity outcomes in Southeast Asian protected areas

Protected areas aim to conserve nature by providing safe havens for biodiversity. However, protection from habitat loss, poaching and other threats, is not guaranteed without adequate investment in their management. Here, we examine the relationship between management effectiveness using the Management Effectiveness Tracking Tool (METT) and trends of 79 populations of mammals and birds in 12 Southeast Asian protected areas from Cambodia, Indonesia, Thailand and Vietnam. Despite the negative influence of corruption on species population change, we find evidence that adequate financial and human resourcing are important determinants in achieving good biodiversity outcomes. Management resourcing, national government transparency and body size collectively explain 29% of the variation in animal population trends in our model. Our paper contributes to a growing evidence base linking management resourcing shortfalls to declining biodiversity populations in protected areas. Our key findings are relevant to international funding agencies, governments and NGOs, to aid decision making around the allocation of conservation resources in Southeast Asia.

Is harvest size a valid indirect measure of abundance for evaluating the population size of game animals using harvest‐based estimation?

Indirect measures of abundance are essential for evaluating temporal and spatial trends in animal populations under hunting pressure and hence for evaluating the impact of hunting on the population stock. Recently, harvest‐based estimation has received attention due to its capacity to estimate population size, hunting mortality and population growth parameters based on the responses of indirect measures to hunting pressure. Although harvest size is a widely used statistic for game animals and its validity as an indirect measure of abundance has been intensively investigated, its applicability to harvest‐based estimation has rarely been studied. In this study, we applied a simulation approach to examine the accuracy of harvest‐based estimation when harvest size is used as an indirect measure under different temporal patterns of capture effort (constant, increasing and decreasing). We simulated a dataset using a Poisson‐binomial surplus‐production model that explicitly considers the effect of capture effort on harvest size and tested the estimation accuracy and model identifiability (i.e. whether there is sufficient statistical information in a dataset to specify model parameters) when harvest size is used as an indirect measure. We then compared the estimates with those of the original Poisson‐binomial surplus‐production model. We found that estimates of the population size and intrinsic growth rate were severely biased when the temporal heterogeneity in capture effort was large. When capture effort was constant and harvest size was thus proportional to the population size, on average, only 10% of iterations were identifiable. The use of harvest size as a population index in harvest‐based estimation can result in seriously biased estimates of population size and growth rate or low identifiability of parameters. Our results highlight the importance of monitoring capture effort and unbiased population indices, in addition to harvest sizes, to evaluate the population status of game animals by harvest‐based estimation.

Nonlinear population dynamics are ubiquitous in animals.

Nonlinear dynamics, where a change in the input is not proportional to a change in the output, are often found throughout nature, for example in biochemical kinetics. Because of the complex suite of interacting abiotic and biotic variables present in ecosystems, animal population dynamics are often thought to be driven in a nonlinear, state-dependent fashion. However, so far these have only been identified in model organisms and some natural systems. Here we show that nonlinear population dynamics are ubiquitous in nature. We use nonlinear forecasting to analyse 747 datasets of 228 species to find that insect population trends were highly nonlinear (74%), followed by mammals (58%), bony fish (49%) and birds (35%). This indicates that linear, equilibrium-based model assumptions may fail at predicting population dynamics across a wide range of animal taxa. We show that faster-reproducing animals are more likely to have nonlinear and high-dimensional dynamics, supporting past ecological theory. Lastly, only a third of time series were predictable beyond two years; therefore, the ability to predict animal population trends using these methods may be limited. Our results suggest that the complex dynamics necessary to cause regime shifts and other transitions may be inherent in a wide variety of animals.

Declining Ungulate Populations in an African Rainforest: Evidence From Local Knowledge, Ecological Surveys, and Bushmeat Records

Human activities alter the composition and abundance of wildlife populations. A common awareness of these changes by stakeholders, including local people is essential for sustainable management. Hunters (n= 255) from two adjacent community hunting zones (CHZs) in Southeast Cameroon were interviewed about the species composition of the animals caught in snare traps during their beginnings in hunting and in 2015- 2016. The comparison of the trends in game composition to those from transect surveys and bushmeat records conducted in the area since the nineties revealed the followings: (1) hunters are aware of the coarse changes in prey abundance, even for the species for which population density is difficult to estimate using classic survey methods; (2) in southeast Cameroon and in forests regions with similar fauna, the bay duiker and the Peter’s duiker are clearly more abundant than the white-bellied and black fronted duiker; (3) the two sites surveyed are under different stages of prey depletion trajectory, and (4) the ranking of prey abundance by local hunters is consistent with village-based bushmeat records and is likely to reflect more the species compositions in anthropogenic forest mosaics, where hunting pressure is higher. Hunters’ interviews constitute a valuable means to rapidly assess the trends in animal populations. However, the discrepancies between perceptions and prey composition in remote forest areas draw attention to the need of caution when using local knowledge to generalize trends in fauna assemblages over large geographical scales.

Contrasting impacts of precipitation on Mediterranean birds and butterflies

The climatic preferences of the species determine to a large extent their response to climate change. Temperature preferences have been shown to play a key role in driving trends in animal populations. However, the relative importance of temperature and precipitation preferences is still poorly understood, particularly in systems where ecological processes are strongly constrained by the amount and timing of rainfall. In this study, we estimated the role played by temperature and precipitation preferences in determining population trends for birds and butterflies in a Mediterranean area. Trends were derived from long-term biodiversity monitoring data and temperature and precipitation preferences were estimated from species distribution data at three different geographical scales. We show that population trends were first and foremost related to precipitation preferences both in birds and in butterflies. Temperature preferences had a weaker effect on population trends, and were significant only in birds. The effect of precipitation on population trends operated in opposite directions in the two groups of species: butterfly species from arid environments and bird species from humid habitats are decreasing most. Our results indicate that, although commonly neglected, water availability is likely an important driver of animal population change in the Mediterranean region, with highly contrasting impacts among taxonomical groups.

Local Knowledge and Perceptions of Animal Population Abundances by Communities Adjacent to the Northern Gonarezhou National Park, Zimbabwe

Understanding animal abundances and population trends is a fundamental goal of ecology. The aim of this study was to examine local ecological knowledge (LEK) held by local people bordering the northern Gonarezhou National Park (GNP), Zimbabwe, concerning domestic and wild animal species abundances and perceived population trends, in order to evaluate the possible contribution of LEK to wildlife conservation and management. Data were collected through interviews using a semi-structured questionnaire from 236 local people in communities adjacent to the northern GNP from December 2010 to May 2011. The results show that perceptions of domestic animal population trends were mixed, with 44% of the respondents perceiving an increase, 36% perceiving a decline, and 20% perceiving that domestic animal populations had remained the same between 2000 and 2010. Furthermore, about 76% of the respondents perceived that wild animal abundances had increased, 15% perceived a decline, and 9% perceived that wild animal abundances had remained the same in GNP between 2000 and 2010. Responses on perceptions of animal population trends were to a great extent in line with recorded population trends from conventional scientific studies. The study results suggest that LEK may serve as a valuable source of ecological information and could compliment scientific information for wildlife conservation and management, particularly in community-based natural resources management programmes.

Understanding subarctic wildlife in Eastern James Bay under changing climatic and socio-environmental conditions: bringing together Cree hunters' ecological knowledge and scientific observations

The Canadian Subarctic is undergoing climatic and environmental changes which are leading to wide-ranging implications for wildlife, ecosystems and aboriginal communities. Through their long-term experience and observations, Cree hunters of the Eastern James Bay are aware of the local manifestations of changes to animal ecology. This article presents and analyses Cree observations of the effects of altering climatic and environmental conditions on animals and their habitat. Cree Trappers Association (CTA) members are witnessing the appearance of pioneer species, changes in animal population trends, migration patterns and distribution, animal behavior, health and habitat which in turn has impacted Cree traditional subsistence activities. Their observations have the potential to fill gaps in wildlife research for subarctic Canada and could serve to influence culturally appropriate environmental change adaptation strategies. The climate change application in the GeoPortal of Eeyou Istchee – a community-based geospatial information tool developed by the CTA to record climate observations and changes in ecosystem is presented in this article denoting the engagement of the Cree in subarctic research. This article contrasts Cree hunters' observation with scientific knowledge and identifies challenges and areas of convergence between scientific and indigenous expertise for investigating animal ecology under a changing climate in the Subarctic.

Protecting endangered species: When are shoot-on-sight policies the only viable option to stop poaching?

Protecting endangered species that offer poachers from low-income countries high economic benefits remains a policy challenge. A broadly applicable economic model of poaching shows why CITES international bans have not always been successful, especially in situations where black markets exist and nonpoaching wages are low. In these situations, poachers may have nothing left to lose, since low nonpoaching wages impose a practical cap on the potential economic costs of fines and imprisonment. Thus, the model suggests “shoot-on-sight” policies as the only viable option. Trends in animal populations appear to support the efficacy of the shoot-on-sight policies, which also suggests an inherent value of life traditionally not captured in Value of a Statistical Life estimates.

Shifting trends: detecting environmentally mediated regulation in long-lived marine vertebrates using time-series data

Assessing the status and trends in animal populations is essential for effective species conservation and management practices. However, unless time-series abundance data demonstrate rapid and reliable fluctuations, objective appraisal of directionality of trends is problematic. We adopted a multiple-working hypotheses approach based on information-theoretic and Bayesian multi-model inference to examine the population trends and form of intrinsic regulation demonstrated by a long-lived species, the southern elephant seal. We also determined the evidence for density dependence in 11 other well-studied marine mammal species. (1) We tested the type of population regulation for elephant seals from Marion Island (1986-2004) and from 11 other marine mammal species, and (2) we described the trends and behavior of the 19-year population time series at Marion Island to identify changes in population trends. We contrasted five plausible trend models using information-theoretic and Bayesian-inference estimates of model parsimony. Our analyses identified two distinct phases of population growth for this population with the inflexion occurring in 1998. Thus, the population decreased between 1986 and 1997 (-3.7% per annum) and increased between 1997 and 2004 (1.9% per annum). An index of environmental stochasticity, the Southern Oscillation Index, explained some of the variance in r and N. We determined analytically that there was good evidence for density dependence in the Marion Island population and that density dependence was widespread among marine mammal species (67% of species showed evidence for population regulation). This approach demonstrates the potential functionality of a relatively simple technique that can be applied to short time series to identify the type of regulation, and the uncertainty associated with the phenomenon, operating in populations of large mammals.

A multi-model framework for simulating wildlife population response to land-use and climate change

Reliable assessments of how human activities will affect wildlife populations are essential for making scientifically defensible resource management decisions. A principle challenge of predicting effects of proposed management, development, or conservation actions is the need to incorporate multiple biotic and abiotic factors, including land-use and climate change, that interact to affect wildlife habitat and populations through time. Here we demonstrate how models of land-use, climate change, and other dynamic factors can be integrated into a coherent framework for predicting wildlife population trends. Our framework starts with land-use and climate change models developed for a region of interest. Vegetation changes through time under alternative future scenarios are predicted using an individual-based plant community model. These predictions are combined with spatially explicit animal habitat models to map changes in the distribution and quality of wildlife habitat expected under the various scenarios. Animal population responses to habitat changes and other factors are then projected using a flexible, individual-based animal population model. As an example application, we simulated animal population trends under three future land-use scenarios and four climate change scenarios in the Cascade Range of western Oregon. We chose two birds with contrasting habitat preferences for our simulations: winter wrens ( Troglodytes troglodytes), which are most abundant in mature conifer forests, and song sparrows ( Melospiza melodia), which prefer more open, shrubby habitats. We used climate and land-use predictions from previously published studies, as well as previously published predictions of vegetation responses using FORCLIM, an individual-based forest dynamics simulator. Vegetation predictions were integrated with other factors in PATCH, a spatially explicit, individual-based animal population simulator. Through incorporating effects of landscape history and limited dispersal, our framework predicted population changes that typically exceeded those expected based on changes in mean habitat suitability alone. Although land-use had greater impacts on habitat quality than did climate change in our simulations, we found that small changes in vital rates resulting from climate change or other stressors can have large consequences for population trajectories. The ability to integrate bottom-up demographic processes like these with top-down constraints imposed by climate and land-use in a dynamic modeling environment is a key advantage of our approach. The resulting framework should allow researchers to synthesize existing empirical evidence, and to explore complex interactions that are difficult or impossible to capture through piecemeal modeling approaches.

Using simple species lists to monitor trends in animal populations: new methods and a comparison with independent data

AbstractThere is an urgent need to develop simple and inexpensive methods for monitoring wildlife populations in resource‐poor countries. List‐based methods have been advocated as simple yet potentially useful biodiversity monitoring tools, and systems have recently been launched in a number of countries to collect species lists. We attempt to advance the use of systematic list‐based monitoring by (1) suggesting improvements to the way in which list reporting rates are calculated; (2) assessing the extent to which degrading effort‐corrected measures of abundance into simple species lists results in loss of information on population trends; (3) comparing long‐term trends in list reporting rates with population trends from a wholly independent monitoring scheme. Daily species lists of birds were derived from regular trapping at a nature reserve in southern England. Most species showed a strong correlation across years between the proportion of lists on which they occurred, adjusted for list length (adjusted list reporting rate; ALRR), and an effort‐corrected measure of abundance (captures per unit effort; CPUE). ALRR revealed almost as much about annual variation in abundance as CPUE for all but the most frequently captured species. Long‐term (>20 years) trends in ALRRs at the nature reserve were positively correlated with UK national population trends recorded over the same period by an independent, labour‐intensive monitoring scheme that counted birds at a large number of widely spread sites. Our results support previous claims that simple species lists could generate data useful for monitoring long‐term population trends, particularly where such lists are collected systematically. However, further research on the efficiency of list reporting rates relative to more sophisticated methods is necessary, before list‐based methods can be advocated for dedicated monitoring schemes in resource‐poor regions.

Notes and records

Sustainable use and management of resources require regular monitoring. In the case of animals, their numbers and distributions are important in determining future trends. The data can also be used for planning and management needs such as habitat use and design of park boundaries ( Norton-Griffiths, 1978). Aerial surveys in East Africa have collected data on animal numbers and other environmental parameters coinciding with wet, intermediate and dry seasons and hence determining animal movements in relation to their food supply ( Western, 1975; Norton-Griffiths, 1978; Sinclair & Norton-Griffiths, 1979). Population trends of animals and their food supply has a bearing on their sustained management in an ecosystem as noted by Kalikawe & Kgathi (1993), Lamprey (1984), Kahurananga (1981), Western (1973) among others. The Department of Resource Surveys and Remote Sensing has been conducting aerial surveys in Ewaso Nyiro basin since 1977 and the cardinal objective of this paper is to present and explain an analysis of animal population trends in this basin spanning a period of 20 years, which is invaluable to the sustainable management of the basin’s biodiversity.