Per Lundberg

Global patterns of diversity and community structure in marine bacterioplankton

Because of their small size, great abundance and easy dispersal, it is often assumed that marine planktonic microorganisms have a ubiquitous distribution that prevents any structured assembly into local communities. To challenge this view, marine bacterioplankton communities from coastal waters at nine locations distributed world‐wide were examined through the use of comprehensive clone libraries of 16S ribosomal RNA genes, used as operational taxonomic units (OTU). Our survey and analyses show that there were marked differences in the composition and richness of OTUs between locations. Remarkably, the global marine bacterioplankton community showed a high degree of endemism, and conversely included few cosmopolitan OTUs. Our data were consistent with a latitudinal gradient of OTU richness. We observed a positive relationship between the relative OTU abundances and their range of occupation, i.e. cosmopolitans had the largest population sizes. Although OTU richness differed among locations, the distributions of the major taxonomic groups represented in the communities were analogous, and all local communities were similarly structured and dominated by a few OTUs showing variable taxonomic affiliations. The observed patterns of OTU richness indicate that similar evolutionary and ecological processes structured the communities. We conclude that marine bacterioplankton share many of the biogeographical and macroecological features of macroscopic organisms. The general processes behind those patterns are likely to be comparable across taxa and major global biomes.

ROBUST DECISION-MAKING UNDER SEVERE UNCERTAINTY FOR CONSERVATION MANAGEMENT

In conservation biology it is necessary to make management decisions for endangered and threatened species under severe uncertainty. Failure to acknowledge and treat uncertainty can lead to poor decisions. To illustrate the importance of considering uncertainty, we reanalyze a decision problem for the Sumatran rhino, Dicerorhinus sumatrensis, using information-gap theory to propagate uncertainties and to rank management options. Rather than requiring information about the extent of parameter uncertainty at the outset, information-gap theory addresses the question of how much uncertainty can be tolerated before our decision would change. It assesses the robustness of decisions in the face of severe uncertainty. We show that different management decisions may result when uncertainty in utilities and probabilities are considered in decision-making problems. We highlight the importance of a full assessment of uncertainty in conservation management decisions to avoid, as much as possible, undesirable outcomes.

Population dynamic consequences of delayed life-history effects

Evidence from wildlife and human populations indicates that conditions during early development can have marked effects on the subsequent performance of individuals and cohorts. Likewise, the effects of maternal and, more generally, parental environments can be transferred among individuals between generations. These delayed life-history effects are found consistently and suggestions have been made that they can be one source of both variability and of delayed density dependence in population dynamics. Assessments of several different time series indicate that population variability and delayed density dependence are common and that understanding the mechanisms giving rise to them is crucial for the interpretation and application of such models to basic and applied research. Therefore, it is necessary to assess the different ways in which history in the life history might give rise to variability and delayed density dependence in population dynamics. Here, we build on recent appraisals of the pervasive influence of past environmental conditions on current and future fitness and link the details of these life-history studies to classic features of population dynamics.

Individual behavior and community dynamics

1 Introduction.- 1.1 Objectives.- 1.2 Topics to be Covered.- 1.3 Predator-Prey Dynamics.- 1.4 Competition.- 1.5 Summary.- 2 Diet Selection.- 2.1 Nutrient-Maximizing Diets.- 2.1.1 Experimental Evidence for Optimal Diets.- 2.1.2 Partial Preferences.- 2.1.3 Diet Selection and the Functional Response.- 2.1.4 Experimental Tests of the Functional Response.- 2.1.5 Diet Choice and Population Dynamics.- 2.2 Evolutionary Dynamics of Diet Selection.- 2.3 Balanced Nutrient Diets.- 2.3.1 Experimental Evidence for Balanced Diets.- 2.3.2 Balanced Diets and Population Dynamics.- 2.4 Summary.- 3 Prey Defense.- 3.1 Types of Defenses.- 3.2 Defense Effects and Population Parameters.- 3.3 Parameter Effects on Dynamics.- 3.4 Time Allocation.- 3.4.1 Risk-Sensitive Prey.- 3.4.2 3-Link System.- 3.5 Optimal Defense.- 3.5.1 Perfectly Timed Induced Defense.- 3.5.2 Lagged Induced Defense.- 3.6 Summary.- 4 Habitat Use and Spatial Structure.- 4.1 Habitat Variation.- 4.2 Energy-Maximizing Habitat Use.- 4.2.1 Experimental Evidence for Optimal Habitat Choice.- 4.2.2 Habitat Choice and Predator-Prey Dynamics.- 4.2.3 Habitat Choice and Competitive Dynamics.- 4.3 Evasion of Predators by Prey.- 4.3.1 Experimental Evidence of Predator Evasion.- 4.3.2 Food Chain Dynamics.- 4.4 Spatial Structure.- 4.4.1 Experimental Evidence of Optimal Patch Use.- 4.4.2 Patchy Predator-Prey Dynamics.- 4.4.3 Experimental Evidence of Patchy Predator-Prey Dynamics.- 4.5 Summary.- 5 Size-Selective Predation.- 5.1 Diet Selection Model.- 5.1.1 Self-Thinning.- 5.1.2 Size-Dependent Consumption.- 5.1.3 Size-Selection and Population Dynamics.- 5.2 Partial Predation Model.- 5.2.1 Consumption Model.- 5.2.2 Partial Predation and Population Dynamics.- 5.3 The Size Structure Challenge.- 5.4 Summary.- 6 Interference and Territoriality.- 6.1 Interference.- 6.1.1 Interference and Population Dynamics.- 6.1.2 Social Structure and Interference Levels.- 6.1.3 Spatial Structure and Interference.- 6.2 Territoriality.- 6.2.1 Optimal Territory Size.- 6.2.2 Evidence for Optimal Territory Size.- 6.2.3 Optimal Territory Size and Population Dynamics.- 6.2.4 Systematic Foraging.- 6.2.5 Central-Place Foraging and Prey Spatial Refugia.- 6.2.6 Central-Place Foraging and Population Dynamics.- 6.3 Summary.- 7 Epilogue.- References.

Noise Colour and the Risk of Population Extinctions

A recurrent problem in ecology and conservation biology is to estimate the risk of population extinctions. Extinction probabilities are not only imperative for conservation and management, but may also elucidate basic mechanisms of the regulation of natural populations (Burgman et al. 1993; Pimm 1994). The usual way of modelling stochastic influence on population dynamics has been to assume that the external noise is uncorrelated. This means that each and every randomly drawn noise value is totally independent on previous ones. This is what is generally called ‘white’ noise. However, the noise itself can be temporally autocorrelated. That is, the values of the random numbers used in the noise process will depend on previous ones. Here we show that the autocorrelation, or colour, of the external noise assumed to influence population dynamics strongly modifies estimated extinction probabilities. For positively autocorrelated (‘red’) noise, the risk of extinction clearly decreases the stronger the autocorrelation is, Negatively autocorrelated (‘blue’) noise is more ambiguously related to extinction probability. Thus, the commonly assumed white noise in population modelling will severely bias population extinction risk estimates. Moreover, the extinction probability estimates are also significantly dependent on model structure which calls for a cautious use of traditional discrete-time models.

Estimating individual contributions to population growth: evolutionary fitness in ecological time

Ecological and evolutionary change is generated by variation in individual performance. Biologists have consequently long been interested in decomposing change measured at the population level into contributions from individuals, the traits they express and the alleles they carry. We present a novel method of estimating individual contributions to population growth and changes in distributions of quantitative traits and alleles. An individuals contribution to population growth is an individuals realized annual fitness. We demonstrate how the quantities we develop can be used to address a range of empirical questions, and provide an application to a detailed dataset of Soay sheep. The approach provides results that are consistent with those obtained using lifetime estimates of individual performance, yet is substantially more powerful as it allows lifetime performance to be decomposed into annual survival and fecundity contributions.

Herbivore avoidance by association: vole and hare utilization of woody plants

The probability that an individual plant will be attacked by a herbivore depends not only on the characteristics of the individual plant, but also on the quality and abundance of its neighbours. However, plants have been reported to receive protection from herbivory both when associated with plants of higher and lower palatability (the attractant-decoy and repellent-plant hypotheses, respectively), and there are no mechanistic explanation for these different outcomes of plant spatial association. We used patch-use theory (marginal-value theorem) to predict under which circumstances we should expect plants to gain protection from herbivory due to association with other plants

A Theory of Partial Migration

In this article we develop a game-theoretical approach to the study of evolutionarily stable partial migration, applicable to both deterministic and stochastic population models. We assume that partial migration is related to the overwintering strategies of animals: a fraction of the population overwinters locally, while another fraction migrates to other overwintering sites. We show that partial migration may arise owing to density-dependent overwintering survival and that environmental uncertainty does not need to be assumed. We also show that, when there are differences in the reproductive successes between the migratory and nonmigratory strategies, then the evolutionarily stable strategy (ESS) may be very sensitive with respect to these differences. Furthermore, when there are differences in the reproductive successes between the migratory and nonmigratory strategies, then applying the same behavior throughout life may not be an ESS (i.e., as the individual grows older, it tends to change from migration to nonmigration). On the other hand, when there are differences in the reproductive successes among ages, then this change in strategies with age is not expected. Finally, we show that uncertainty may or may not bias the ESS fraction of migratory animals depending on whether uncertainties affect the average population levels.

POPULATION VARIABILITY IN SPACE AND TIME : THE DYNAMICS OF SYNCHRONOUS POPULATION FLUCTUATIONS

Empirical studies have shown that animal populations from a wide array of taxa exhibit spatial patterns of correlation in fluctuating abundance. In the search for explanations for this phenomenon it has been proposed that subpopulation interactions in the form of spatial dispersal, or variability in external factors, such as weather, would be the crucial driving forces responsible for spatial synchrony. Nevertheless, dispersal and external factors have been shown to produce different patterns of synchrony. We show here that observed patterns in synchronous dynamics can be reproduced by using a spatially linked population model. Further, we analyse how local and global environmental stochasticity and dispersal influence the pattern of spatial synchrony. We contrast our theoretical results with data on long-term dynamics of North American game animals and emphasize that the data and our spatial population dynamics models are compatible.

Dispersal, Migration, and Offspring Retention in Saturated Habitats

We examine the evolutionary stability of year‐round residency in territorial populations, where breeding sites are a limiting resource. The model links individual life histories to the population‐wide competition for territories and includes spatial variation in habitat quality as well as a potential parent‐offspring conflict over territory ownership. The general form of the model makes it applicable to the evolution of dispersal, migration, partial migration, and delayed dispersal (offspring retention). We show that migration can be evolutionarily stable only if year‐round residency in a given area would produce a sink population, where mortality exceeds reproduction. If this applies to a fraction of the breeding habitat only, partial migration is expected to evolve. In the context of delayed dispersal, habitat saturation has been argued to form an ecological constraint on independent breeding, which favors offspring retention and cooperative breeding. We show that habitat saturation must be considered as a dynamic outcome of birth, death, and dispersal rates in the population, rather than an externally determined constraint. Although delayed dispersal often associates with intense competition for territories, life‐history traits have direct effects on stable dispersal strategies, which can often override the effect of habitat saturation. As an example, high survival of floaters selects against delayed dispersal, even though it increases the number of competitors for each breeding vacancy (the “habitat saturation factor”). High survival of territory owners, by contrast, generally favors natal philopatry. We also conclude that spatial variation in habitat quality only rarely selects for delayed dispersal. Within a population, however, offspring retention is more likely in high‐quality territories.