Nathalie Pettorelli

Essential Biodiversity Variables

A global system of harmonized observations is needed to inform scientists and policy-makers. Reducing the rate of biodiversity loss and averting dangerous biodiversity change are international goals, reasserted by the Aichi Targets for 2020 by Parties to the United Nations (UN) Convention on Biological Diversity (CBD) after failure to meet the 2010 target (1, 2). However, there is no global, harmonized observation system for delivering regular, timely data on biodiversity change (3). With the first plenary meeting of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) soon under way, partners from the Group on Earth Observations Biodiversity Observation Network (GEO BON) (4) are developing—and seeking consensus around—Essential Biodiversity Variables (EBVs) that could form the basis of monitoring programs worldwide.

Empirical evidence of density-dependence in populations of large herbivores

Density‐dependence is a key concept in population dynamics. Here, we review how body mass and demographic parameters vary with population density in large herbivores. The demographic parameters we consider are age‐ and sex‐specific reproduction, survival and dispersal. As population density increases, the body mass of large herbivores typically declines, affecting individual performance traits such as age of first reproduction and juvenile survival. We documented density‐dependent variations in reproductive rates for many species from the Arctic to subtropical zones, both with and without predation. At high density, a trade‐off between growth and reproduction delays the age of primiparity and often increases the costs of reproduction, decreasing both survival and future reproductive success of adult females. Density‐dependent preweaning juvenile survival occurs more often in polytocous than monotocous species, while the effects of density on post‐weaning juvenile survival are independent of litter size. Responses of adult survival to density are much less marked than for juvenile survival, and may be exaggerated by density‐dependent changes in age structure. The role of density‐dependent dispersal in population dynamics remains uncertain, because very few studies have examined it. For sexually dimorphic species, we found little support for higher sensitivity to increasing density in the life history traits of males compared to females, except for young age classes. It remains unclear whether males of dimorphic species are sensitive to male density, female density or a combination of both. Eberhardts model predicting a sequential effect of density on demographic parameters (from juvenile survival to adult survival) was supported by 9 of 10 case studies. In addition, population density at birth can also lead to cohort effects, including a direct effect on juvenile survival and longterm effects on average cohort performance as adults. Density effects typically interact with weather, increasing in strength in years of harsh weather. For some species, the synchronization between plant phenology and reproductive cycle is a key process in population dynamics. The timing of late gestation as a function of plant phenology determines whether density‐dependence influences juvenile survival or adult female reproduction. The detection of density‐dependence can be made difficult by nonlinear relationships with density, high sampling variability, lagged responses to density changes, changes in population age structure, and temporal variation in the main factors limiting population growth. The negative feedbacks of population size on individual performance, and hence on life history traits, are thus only expected in particular ecological contexts and are most often restricted to certain age‐specific demographic traits.

Early onset of vegetation growth vs. rapid green-up: impacts on juvenile mountain ungulates.

Seasonal patterns of climate and vegetation growth are expected to be altered by global warming. In alpine environments, the reproduction of birds and mammals is tightly linked to seasonality; therefore such alterations may have strong repercussions on recruitment. We used the normalized difference vegetation index (NDVI), a satellite-based measurement that correlates strongly with aboveground net primary productivity, to explore how annual variations in the timing of vegetation onset and in the rate of change in primary production during green-up affected juvenile growth and survival of bighorn sheep (Ovis canadensis), Alpine ibex (Capra ibex), and mountain goats (Oreamnos americanus) in four different populations in two continents. We indexed timing of onset of vegetation growth by the integrated NDVI (INDVI) in May. The rate of change in primary production during green-up (early May to early July) was estimated as (1) the maximal slope between any two successive bimonthly NDVI values during this period and (2) the slope in NDVI between early May and early July. The maximal slope in NDVI was negatively correlated with lamb growth and survival in both populations of bighorn sheep, growth of mountain goat kids, and survival of Alpine ibex kids, but not with survival of mountain goat kids. There was no effect of INDVI in May and of the slope in NDVI between early May and early July on juvenile growth and survival for any species. Although rapid changes in NDVI during the green-up period could translate into higher plant productivity, they may also lead to a shorter period of availability of high-quality forage over a large spatial scale, decreasing the opportunity for mountain ungulates to exploit high-quality forage. Our results suggest that attempts to forecast how warmer winters and springs will affect animal population dynamics and life histories in alpine environments should consider factors influencing the rate of changes in primary production during green-up and the timing of vegetation onset.

Biodiversity redistribution under climate change : Impacts on ecosystems and human well-being

Consequences of shifting species distributions Climate change is causing geographical redistribution of plant and animal species globally. These distributional shifts are leading to new ecosystems and ecological communities, changes that will affect human society. Pecl et al. review these current and future impacts and assess their implications for sustainable development goals. Science, this issue p. eaai9214 BACKGROUND The success of human societies depends intimately on the living components of natural and managed systems. Although the geographical range limits of species are dynamic and fluctuate over time, climate change is impelling a universal redistribution of life on Earth. For marine, freshwater, and terrestrial species alike, the first response to changing climate is often a shift in location, to stay within preferred environmental conditions. At the cooler extremes of their distributions, species are moving poleward, whereas range limits are contracting at the warmer range edge, where temperatures are no longer tolerable. On land, species are also moving to cooler, higher elevations; in the ocean, they are moving to colder water at greater depths. Because different species respond at different rates and to varying degrees, key interactions among species are often disrupted, and new interactions develop. These idiosyncrasies can result in novel biotic communities and rapid changes in ecosystem functioning, with pervasive and sometimes unexpected consequences that propagate through and affect both biological and human communities. ADVANCES At a time when the world is anticipating unprecedented increases in human population growth and demands, the ability of natural ecosystems to deliver ecosystem services is being challenged by the largest climate-driven global redistribution of species since the Last Glacial Maximum. We demonstrate the serious consequences of this species redistribution for economic development, livelihoods, food security, human health, and culture, and we document feedbacks on climate itself. As with other impacts of climate change, species range shifts will leave “winners” and “losers” in their wake, radically reshaping the pattern of human well-being between regions and different sectors and potentially leading to substantial conflict. The pervasive impacts of changes in species distribution transcend single systems or dimensions, with feedbacks and linkages between multiple interacting scales and through whole ecosystems, inclusive of humans. We argue that the negative effects of climate change cannot be adequately anticipated or prepared for unless species responses are explicitly included in decision-making and global strategic frameworks. OUTLOOK Despite mounting evidence for the pervasive and substantial impacts of a climate-driven redistribution of Earth’s species, current global goals, policies, and international agreements fail to account for these effects. With the predicted intensification of species movements and their diverse societal and environmental impacts, awareness of species “on the move” should be incorporated into local, regional, and global assessments as standard practice. This will raise hope that future targets—whether they be global sustainability goals, plans for regional biodiversity maintenance, or local fishing or forestry harvest strategies—can be achievable and that society is prepared for a world of universal ecological change. Human society has yet to appreciate the implications of unprecedented species redistribution for life on Earth, including for human lives. Even if greenhouse gas emissions stopped today, the responses required in human systems to adapt to the most serious effects of climate-driven species redistribution would be massive. Meeting these challenges requires governance that can anticipate and adapt to changing conditions, as well as minimize negative consequences. As the global climate changes, human well-being, ecosystem function, and even climate itself are increasingly affected by the shifting geography of life. Climate-driven changes in species distributions, or range shifts, affect human well-being both directly (for example, through emerging diseases and changes in food supply) and indirectly (by degrading ecosystem health). Some range shifts even create feedbacks (positive or negative) on the climate system, altering the pace of climate change. Distributions of Earth’s species are changing at accelerating rates, increasingly driven by human-mediated climate change. Such changes are already altering the composition of ecological communities, but beyond conservation of natural systems, how and why does this matter? We review evidence that climate-driven species redistribution at regional to global scales affects ecosystem functioning, human well-being, and the dynamics of climate change itself. Production of natural resources required for food security, patterns of disease transmission, and processes of carbon sequestration are all altered by changes in species distribution. Consideration of these effects of biodiversity redistribution is critical yet lacking in most mitigation and adaptation strategies, including the United Nation’s Sustainable Development Goals.

Variations in adult body mass in roe deer: the effects of population density at birth and of habitat quality

Body mass is a key determinant of fitness components in many organisms, and adult mass varies considerably among individuals within populations. These variations have several causes, involve temporal and spatial factors, and are not yet well understood. We use long‐term data from 20 roe deer cohorts (1977‐96) in a 2600 ha study area (Chizé, western France) with two habitats contrasting in quality (rich oak forest in the North versus poor beech forest in the South) to analyse the effects of both cohort and habitat quality on adult mass (i.e. median body mass between 4 and 10 years of age) of roe deer (Capreolus capreolus). Cohort strongly influenced the adult body mass of roe deer in both sexes: males born in 1994 were 5.2 kg heavier when aged between 4 and 10 years old than males born in 1986, while females born in 1995 were 4.7 kg heavier between 4 and 10 years old than females born in 1982. For a given cohort, adult males were, on average, 0.9 kg heavier in the rich oak forest than in the poor beech forest. A similar trend occurred for adult females (0.5 kg heavier in the oak forest). The effects of cohort and habitat were additive and accounted for ca. 40% of the variation observed in the adult mass of roe deer at Chizé (males: 41.2%; females: 40.2%). Population density during the spring of the birth accounted for about 35% of cohort variation, whereas rainfall in May‐June had no effect. Such delayed effects of density at birth on adult body mass probably affect population dynamics, and might constitute a mechanism by which delayed density‐dependence occurs in ungulate populations.

Importance of climatological downscaling and plant phenology for red deer in heterogeneous landscapes

Understanding how climate influences ecosystems represents a challenge in ecology and natural resource management. Although we know that climate affects plant phenology and herbivore performances at any single site, no study has directly coupled the topography–climate interaction (i.e. the climatological downscaling process) with large-scale vegetation dynamics and animal performances. Here we show how climatic variability (measured by the North Atlantic oscillation ‘NAO’) interacts with local topography in determining the vegetative greenness (as measured by the normalized difference vegetation index ‘NDVI’) and the body masses and seasonal movements of red deer (Cervus elaphus) in Norway. Warm springs induced an earlier onset of vegetation, resulting in earlier migration and higher body masses. Increasing values of the winter-NAO corresponded to less snow at low altitude (warmer, more precipitation results in more rain), but more snow at high altitude (colder, more precipitation corresponds to more snow) relative to winters with low winter-NAO. An increasing NAO thus results in a spatially more variable phenology, offering migrating deer an extended period with access to high-quality forage leading to increased body mass. Our results emphasize the importance of incorporating spring as well as the interaction between winter climate and topography when aiming at understanding how plant and animal respond to climate change.

Satellite remote sensing for applied ecologists: opportunities and challenges.

1. Habitat loss and degradation, overexploitation, climate change and the spread of invasive species are drastically depleting the Earths biological diversity, leading to detrimental impacts on ecosystem services and human well-being. 2. Our ability to monitor the state of biodiversity and the impacts of global environmental change on this natural capital is fundamental to designing effective adaptation and mitigation strategies for preventing further loss of biological diversity. This requires the scientific community to assess spatio-temporal changes in the distribution of abiotic conditions (e.g. temperature, rainfall) and in the distribution, structure, composition and functioning of ecosystems. 3. The potential for satellite remote sensing (SRS) to provide key data has been highlighted by many researchers, with SRS offering repeatable, standardized and verifiable information on long-term trends in biodiversity indicators. SRS permits one to address questions on scales inaccessible to ground-based methods alone, facilitating the development of an integrated approach to natural resource management, where biodiversity, pressures to biodiversity and consequences of management decisions can all be monitored. 4. Synthesis and applications. Here, we provide an interdisciplinary perspective on the prospects of satellite remote sensing (SRS) for ecological applications, reviewing established avenues and highlighting new research and technological developments that have a high potential to make a difference in environmental management. We also discuss current barriers to the ecological application of SRS-based approaches and identify possible ways to overcome some of these limitations.

Environmental science: Agree on biodiversity metrics to track from space

Ecologists and space agencies must forge a global monitoring strategy, say Andrew K. Skidmore, Nathalie Pettorelli and colleagues.

The relative role of winter and spring conditions: linking climate and landscape-scale plant phenology to alpine reindeer body mass

The relative importance of winter harshness and early summer foraging conditions are of prime interest when assessing the effect of global warming on artic and mountainous ecosystems. We explored how climate and vegetation onset (satellite-derived Normalized Difference Vegetation Index data) determined individual performance in three reindeer populations (data on 27 814 calves sampled over 11 years). Snow conditions, spring temperatures and topography were the main determinants of the onset of the vegetation. An earlier onset positively affected the body mass of calves born the following autumn, while there was no significant direct negative impact of the previous winter. This study underlines the major impact of winter and spring climatic conditions, determining the spring and summer food availability, and the subsequent growth of calves among alpine herbivores.

Severe drought and calf survival in elephants

Climate change in Africa is expected to lead to a higher occurrence of severe droughts in semi-arid and arid ecosystems. Understanding how animal populations react to such events is thus crucial for addressing future challenges for wildlife management and conservation. We explored how gender, age, mothers experience and family group characteristics determined calf survival in an elephant population during a severe drought in Tanzania in 1993. Young males were particularly sensitive to the drought and calf loss was higher among young mothers than among more experienced mothers. We also report high variability in calf mortality between different family groups, with family groups that remained in the National Park suffering heavy calf loss, compared with the ones that left the Park. This study highlights how severe droughts can dramatically affect early survival of large herbivores and suggests that extreme climatic events might act as a selection force on vertebrate populations, allowing only individuals with the appropriate behaviour and/or knowledge to survive.