Nigel G. Yoccoz

Monitoring of biological diversity in space and time

Monitoring programmes are being used increasingly to assess spatial and temporal trends of biological diversity, with an emphasis on evaluating the efficiency of management policies. Recent reviews of the existing programmes, with a focus on their design in particular, have highlighted the main weaknesses: the lack of well-articulated objectives and the neglect of different sources of error in the estimation of biological diversity. We review recent developments in methods and designs that aim to integrate sources of error to provide unbiased estimates of change in biological diversity and to suggest the potential causes.

TEMPORAL VARIATION IN SURVIVAL OF MAMMALS: A CASE OF ENVIRONMENTAL CANALIZATION?

In an age- or stage-structured population, a given change on a proportional scale of different fitness components has different effects on the population growth rate. Because earlier studies have shown that variability is selectively disadvantageous for long-lived iteroparous species, fitness components whose variation has greatest impact on the population growth rate are expected to be canalized against temporal variability. We present here a test for such a canalization of fitness components most influential for population growth. If canalization occurs, (1) within a given population the variance of canalized fitness components should be less than that of noncanalized components, and (2) among populations an inverse relationship should occur between the potential demographic impact of fitness components and their temporal variability. We tested these hypotheses using data on age-dependent survival of ungulates. As expected for long-lived vertebrates, elasticities and sensitivities of adult survival were...

The Response of Terrestrial Ecosystems to Climate Variability Associated with the North Atlantic Oscillation

Climatic factors influence a variety of ecological processes determining patterns of species density and distribution in a wide range of terrestrial ecosystems. We review the effects of the NAO on processes and patterns of terrestrial ecosystems, including both plants and animals. In plants, the NAO index correlates with date of first flowering, tree ring growth and with quality of agricultural crops (wheat and wine grapes). Also, breeding dates are earlier after high NAO index winters for amphibians and birds in Europe. Population dynamical consequences of the NAO have also been reported for birds, and the differential impact of the NAO on two similar species may prevent competitive exclusion. Different effects of the NAO on large herbivore populations have been reported for different regions, depending on limiting factors and the correlation with local weather parameters. The NAO synchronizes population dynamics of lynx and some other carnivore populations in the eastern U.S. Most effects are on an ecological time scale; the evolutionary consequences of long term trends in the NAO are poorly documented. Important for predator and prey dynamics is (1) the disruption of phenology (the match-mismatch hypothesis), (2) that there may be delayed effects (cohort-effects), and (3) that effects of the NAO may interact with other factors such as density. We discuss the challenges related to nonlinearity, of using different climate indices, and how we can progress using these pattern-oriented NAO studies at coarse scales to conduct better process-oriented small-scale experiments.

Climatic extremes improve predictions of spatial patterns of tree species

Understanding niche evolution, dynamics, and the response of species to climate change requires knowledge of the determinants of the environmental niche and species range limits. Mean values of climatic variables are often used in such analyses. In contrast, the increasing frequency of climate extremes suggests the importance of understanding their additional influence on range limits. Here, we assess how measures representing climate extremes (i.e., interannual variability in climate parameters) explain and predict spatial patterns of 11 tree species in Switzerland. We find clear, although comparably small, improvement (+20% in adjusted D2, +8% and +3% in cross-validated True Skill Statistic and area under the receiver operating characteristics curve values) in models that use measures of extremes in addition to means. The primary effect of including information on climate extremes is a correction of local overprediction and underprediction. Our results demonstrate that measures of climate extremes are important for understanding the climatic limits of tree species and assessing species niche characteristics. The inclusion of climate variability likely will improve models of species range limits under future conditions, where changes in mean climate and increased variability are expected.

Nonlinear effects of large-scale climatic variability on wild and domestic herbivores.

Large-scale climatic fluctuations, such as the North Atlantic Oscillation (NAO), have been shown to affect many ecological processes. Such effects have been typically assumed to be linear. Only one study has reported a nonlinear relation; however, that nonlinear relation was monotonic (that is, no reversal). Here we show that there is a strong nonlinear and non-monotonic (that is, reversed) effect of the NAO on body weight during the subsequent autumn for 23,838 individual wild red deer (Cervus elaphus) and 139,485 individual domestic sheep (Ovis aries) sampled over several decades on the west coast of Norway. These relationships are, at least in part, explained by comparable nonlinear and non-monotonic relations between the NAO and local climatic variables (temperature, precipitation and snow depth). The similar patterns observed for red deer and sheep, the latter of which live indoors during winter and so experience a stable energy supply in winter, suggest that the (winter) climatic variability (for which the index is a proxy) must influence the summer foraging conditions directly or indirectly.

Fifty thousand years of Arctic vegetation and megafaunal diet

Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr bp (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25–15 kyr bp), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr bp, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.

Impacts of climate change on the world's most exceptional ecoregions

The current rate of warming due to increases in greenhouse gas (GHG) emissions is very likely unprecedented over the last 10,000 y. Although the majority of countries have adopted the view that global warming must be limited to <2 °C, current GHG emission rates and nonagreement at Copenhagen in December 2009 increase the likelihood of this limit being exceeded by 2100. Extensive evidence has linked major changes in biological systems to 20th century warming. The “Global 200” comprises 238 ecoregions of exceptional biodiversity [Olson DM, Dinerstein E (2002) Ann Mo Bot Gard 89:199–224]. We assess the likelihood that, by 2070, these iconic ecoregions will regularly experience monthly climatic conditions that were extreme in 1961–1990. Using >600 realizations from climate model ensembles, we show that up to 86% of terrestrial and 83% of freshwater ecoregions will be exposed to average monthly temperature patterns >2 SDs (2σ) of the 1961–1990 baseline, including 82% of critically endangered ecoregions. The entire range of 89 ecoregions will experience extreme monthly temperatures with a local warming of <2 °C. Tropical and subtropical ecoregions, and mangroves, face extreme conditions earliest, some with <1 °C warming. In contrast, few ecoregions within Boreal Forests and Tundra biomes will experience such extremes this century. On average, precipitation regimes do not exceed 2σ of the baseline period, although considerable variability exists across the climate realizations. Further, the strength of the correlation between seasonal temperature and precipitation changes over numerous ecoregions. These results suggest many Global 200 ecoregions may be under substantial climatic stress by 2100.

Analysing diet of small herbivores: the efficiency of DNA barcoding coupled with high-throughput pyrosequencing for deciphering the composition of complex plant mixtures

BackgroundIn order to understand the role of herbivores in trophic webs, it is essential to know what they feed on. Diet analysis is, however, a challenge in many small herbivores with a secretive life style. In this paper, we compare novel (high-throughput pyrosequencing) DNA barcoding technology for plant mixture with traditional microhistological method. We analysed stomach contents of two ecologically important subarctic vole species, Microtus oeconomus and Myodes rufocanus, with the two methods. DNA barcoding was conducted using the P6-loop of the chloroplast trn L (UAA) intron.ResultsAlthough the identified plant taxa in the diets matched relatively well between the two methods, DNA barcoding gave by far taxonomically more detailed results. Quantitative comparison of results was difficult, mainly due to low taxonomic resolution of the microhistological method, which also in part explained discrepancies between the methods. Other discrepancies were likely due to biases mostly in the microhistological analysis.ConclusionWe conclude that DNA barcoding opens up for new possibilities in the study of plant-herbivore interactions, giving a detailed and relatively unbiased picture of food utilization of herbivores.

Induced Shift in Ecosystem Productivity? Extensive Scale Effects of Abundant Large Herbivores

Abundant large herbivores can strongly alter vegetation composition, shifting the ecosystem into a lasting state of changed productivity. Previous studies of the effects of abundant reindeer on alpine and arctic vegetation have yielded equivocal results, probably due to differing environmental contexts. To overcome context dependency we devised a large-scale survey in the region of Finnmark, northern Norway, possessing some of the most densely stocked reindeer herds in the world. The effects of reindeer abundance on summer pasture vegetation were assessed by employing a quasi-experimental design, including site fertility as a potential modifier of the reindeer–vegetation interaction. The study design comprised ten pairs of neighboring management districts (encompassing 18,003 km2), where over the two last decades a high-density district on average had reindeer densities more than twice as high and calf weights consistently lower than the low-density district. The abundance of different plant functional groups, ranging from those having facilitating to retarding effects on ecosystem productivity, were quantified by the point intercept method on plots selected according to a hierarchical, stratified random sampling design. Species with strong retarding effects on ecosystem productivity (for example, ericoids) were by far the most abundant. However, we found no consistent effects of reindeer density on their abundance. The most consistent differences between high- and low-density districts were found in plant functional groups with facilitating to neutral effects on ecosystem productivity. In particular, the abundance of N-facilitators, large dicotyledons and grasses were substantially reduced in the high-density districts. However, this reduction was restricted to fertile sites. Thus, reindeer when present at high densities have homogenized the biomass of palatable plants across environmental productivity gradients according to predictions from exploitation ecosystem models. Such reduction of plants with facilitating to neutral effects on ecosystem productivity indicates a reduced state of ecosystem productivity in high-density districts.

Studying Transfer Processes in Metapopulations: Emigration, Migration, and Colonization

Publisher Summary This chapter examines the emigration, migration, and colonization aspects of a transfer process in metapopulations. The transfer of individuals across space is a key process in metapopulations. Metapopulations are often seen as sets of local populations, the very existence of which is dependent on mutual transfer (or exchange) of individuals. Components of transfer rates such as emigration, migration (dispersal), and colonization become critical variables, which need to be approached empirically by different study designs. At the same time, the three transfer stages are clearly linked both methodologically and biologically. Emigration, dispersal, and immigration/colonization must be translated into transfer rates to be used in predictive models at the metapopulation level. Likewise, the three transfer processes are also linked to patch-specific demographic parameters. This chapter draws together the various empirical approaches to the study of transfer processes in a metapopulation context. The limitations and advantages of different approaches are stressed, along with assessment of the lines of inferences that can reliably be drawn from them.