Optimizing Species Richness in Mosaic Landscapes: A Probabilistic Model of Species-Area Relationships

Most landscapes are comprised of multiple habitat types differing in the biodiversity they contain. This is certainly true for human modified landscapes, which are often a mix of habitats managed with different intensity, semi-natural habitats and even pristine habitats. To understand fundamental questions of how the composition of such landscapes affects biodiversity conservation, and to evaluate biodiversity consequences of policies that affect the composition of landscapes, there is a need for models able to translate information on biodiversity from individual habitats to landscape-wide predictions. However, this is complicated by species richness not being additive. We constructed a model to help analyze and solve this problem based on two simple assumptions. Firstly, that a habitat can be characterized by the biological community inhabiting it; i.e., which species occur and at what densities. Secondly, that the probability of a species occurring in a particular unit of land is dictated by its average density in the associated habitats, its spatial aggregation, and the size of the land unit. This model leads to a multidimensional species-area relation (one dimension per habitat). If the goal is to maximize species diversity at the landscape scale (γ-diversity), within a fixed area or under a limited budget, the model can be used to find the optimal allocation of the different habitats. In general, the optimal solution depends on the total size of the species pool of the different habitats, but also their similarity (β-diversity). If habitats are complementary (high β), a mix is usually preferred, even if one habitat is poorer (lower α diversity in one habitat). The model lends itself to economic analyses of biodiversity problems, without the need to monetarize biodiversity value, i.e., cost-effectiveness analysis. Land prices and management costs will affect the solution, such that the model can be used to estimate the number of species gained in relation to expenditure on each habitat. We illustrate the utility of the model by applying it to agricultural landscapes in southern Sweden and demonstrate how empirical monitoring data can be used to find the best habitat allocation for biodiversity conservation within and between landscapes

Population trends of waders on their boreal and arctic breeding grounds in northern Europe

Waders form a conspicuous part of the bird fauna in boreal and arctic areas, where they inhabit forests, wetlands, mires and tundra. These are important breeding areas for a large set of wader species, and may be particularly vulnerable to climate change. However, large-scale and systematic monitoring data from the breeding grounds of boreal and arctic waders are largely lacking. We present population trends for 22 wader species breeding in the boreal and arctic parts of Fennoscandia (Norway, Sweden and Finland) between 2006 and 2018. The trends are based on 9,713 surveys of 1,505 unique routes (6–8 km), each surveyed in at least two years, evenly distributed over an area of ~1 million km2. The trends were significantly negative for three species: Red-necked Phalarope Phalaropus lobatus (–7.9% year-1), Broad-billed Sandpiper Calidris falcinellus (–5.4% year-1), and Whimbrel Numenius phaeopus (–1.3% year-1). The trends were significantly positive for three species: Oystercatcher Haematopus ostralegus (+4.9% year-1), Dunlin Calidris a. alpina (+4.2% year-1) and Wood Sandpiper Tringa glareola (+0.8% year-1). For the remaining species, we found no statistically significant trends. On average, as shown by a multi-species indicator, there was no general change in numbers over time. On 1,539 routes with at least one survey, wader species richness as well as total number of wader pairs increased significantly with increasing latitude. Species population trend was not correlated with breeding latitude, but population trends of long-distance migrants tended to be more negative than those of medium-distance migrants. The recent fortunes of waders breeding in northern Fennoscandia have been more buoyant than those in other parts of Europe, but the trends for some species are worrying. © 2019, International Wader Study Group. All rights reserved.Peer reviewe

Maximum Host Survival at Intermediate Parasite Infection Intensities

BACKGROUND: Although parasitism has been acknowledged as an important selective force in the evolution of host life histories, studies of fitness effects of parasites in wild populations have yielded mixed results. One reason for this may be that most studies only test for a linear relationship between infection intensity and host fitness. If resistance to parasites is costly, however, fitness may be reduced both for hosts with low infection intensities (cost of resistance) and high infection intensities (cost of parasitism), such that individuals with intermediate infection intensities have highest fitness. Under this scenario one would expect a non-linear relationship between infection intensity and fitness. METHODOLOGY/PRINCIPAL FINDINGS: Using data from blue tits (Cyanistes caeruleus) in southern Sweden, we investigated the relationship between the intensity of infection of its blood parasite (Haemoproteus majoris) and host survival to the following winter. Presence and intensity of parasite infections were determined by microscopy and confirmed using PCR of a 480 bp section of the cytochrome-b-gene. While a linear model suggested no relationship between parasite intensity and survival (F = 0.01, p = 0.94), a non-linear model showed a significant negative quadratic effect (quadratic parasite intensity: F = 4.65, p = 0.032; linear parasite intensity F = 4.47, p = 0.035). Visualization using the cubic spline technique showed maximum survival at intermediate parasite intensities. CONCLUSIONS/SIGNIFICANCE: Our results indicate that failing to recognize the potential for a non-linear relationship between parasite infection intensity and host fitness may lead to the potentially erroneous conclusion that the parasite is harmless to its host. Here we show that high parasite intensities indeed reduced survival, but this effect was masked by reduced survival for birds heavily suppressing their parasite intensities. Reduced survival among hosts with low parasite intensities suggests costs of controlling parasite infections; however, the nature of such costs remains to be elucidated

Stabilising selection on immune response in male black grouse Lyrurus tetrix

Illnesses caused by a variety of micro- and macro- organisms can negatively affect individuals’ fitness, leading to the expectation that immunity is under positive selection. However, immune responses are costly and individuals must trade-off their immune response with other fitness components (e.g. survival or reproductive success) meaning that individuals with intermediate response may have the greatest overall fitness. Such a process might be particularly acute in species with strong sexual selection because the condition-dependence of male secondary sexual-traits might lead to striking phenotypic differences amongst males of different immune response levels. We tested whether there is selection on immune response by survival and reproduction in yearling and adult male black grouse (Lyrurus tetrix) following an immune challenge with a novel antigen and tested the hypothesis that sexual signals and body mass are honest signals of the immune response. We show that yearling males with highest immune response to these challenges had higher survival, but the reverse was true for adults. Adults with higher responses had highest mass loss and adult males with intermediate immune response had highest mating success. Tail length was related to baseline response in adults and more weakly in yearlings. Our findings reveal the complex fitness consequences of mounting an immune response across age classes. Such major differences in the direction and magnitude of selection in multiple fitness components is an alternative route underpinning the stabilizing selection of immune responses with an intermediate immune response being optimal

Causes and consequences of blood parasite infections in birds

Parasites are ubiquitous and can cause significant fitness reductions to their hosts. Therefore, selection for the evolution of host resistance should be strong. However, resistance may be costly and should be traded-off against other fitness related traits. Parasites could therefore have a significant impact on the evolution of fitness related characters of their hosts. It has been suggested that the workload put into reproduction is negatively related to the ability to resist parasites and that this trade-off could explain the reduction in future reproduction as a result of current reproductive effort – a trade-off termed the cost of reproduction. I studied whether blood parasites could mediate reproductive costs by examining if altered reproductive effort affected infection levels of a blood parasite (Haemoproteus) and concomitant survival in the blue tit (Parus caeruleus). I found a negative relationship between altered reproductive effort and survival and a positive relationship between reproductive effort and parasite intensity. However, since parasite intensities were not related to survival when controlling for other factors related to the experiment, these parasites could not mediate the reproductive costs found. An alternative way of verifying costs of resistance may be to study selection patterns since the presence of such fitness costs should manifest as stabilising selection on resistance. That is, fitness is not only reduced if hosts are unable to control the parasites, but also if resistance comes with a fitness cost. Indeed, I found that individuals with intermediate parasite intensities had highest survival. I also found that individuals with intermediate immune responsiveness against diphtheria vaccine had highest survival. However, different components of resistance may carry different costs since I found that individuals with the strongest response against another antigen (tetanus) were those that had highest survival. Another finding was that the intensity of infection within one-year-old individuals were significantly related to the rearing conditions experienced during the nestling phase and that the level of infection is repeatable between years. This suggests that parasite resistance is fixed during development and that individuals have limited possibilities to compensate for adverse conditions experienced during the nestling phase. The influence of early development on parasite resistance indicate that maternal effects may be important and one possible route by which the mother could influence offspring immunity may be through the transfer of antibodies via the egg. I found that offspring of mothers that were immunised with a bacterial antigen had higher levels of (and a larger increase in) antibodies at the end of the nestling period compared to offspring of mothers that were not immunised

Natural selection on immune responsiveness in blue tits Parus caeruleus

What is the form of natural selection on immune responsiveness? For a population at evolutionary equilibrium, there are two different scenarios. First, it is generally assumed that immune defense has both benefits and costs. If variation in immune responsiveness is due to variation in how individuals trade off these costs and benefits, one would expect immune responsiveness to be subject to stabilizing selection. Second, it is well known that an individual's immune responsiveness is often dependent on its overall condition. If immune responsiveness is condition-dependent, one would expect immune responsiveness to be under positive directional selection. We would therefore expect that the form of natural selection on immune responsiveness depends on the relative magnitude of these two sources of variation: variation in how individuals trade off the costs and benefits of defense, and variation in condition. We measured primary and secondary antibody responsiveness to diphtheria-tetanus vaccine in blue tits during winter and investigated the relationship between responsiveness and survival to the following breeding season. We use responsiveness to these antigens as measures of an individual's ability or propensity to mount an antibody response in case of an infection. Interestingly, different measures of responsiveness were subject to different selective regimes: primary responsiveness to diphtheria was subject to stabilizing selection, whereas secondary responsiveness to tetanus was subject to positive directional selection. In contrast, there was no significant selection on primary responsiveness to tetanus or secondary responsiveness to diphtheria. The finding of stabilizing selection on a measure of responsiveness is evidence that immune defense can incur fitness costs; a central but little-tested assumption of theories of the ecology and evolution of immunological defense. The finding of directional selection on a measure of responsiveness is consistent with the idea that immune responsiveness is condition-dependent, although we cannot rule out the alternative explanation that the population is not at evolutionary equilibrium with respect to this trait

Immune responsiveness in adult blue tits: heritability and effects of nutritional status during ontogeny

What is the relative contribution of genetic and various environmental factors to variation in the ability to mount an immune response? We measured antibody responsiveness to diphtheria-tetanus vaccine during the winter in free-ranging blue tits with a known nestling history to investigate (1) if nutritional status during the nestling stage has persistent effects on an individual's immune defence and (2) if immune responsiveness is heritable. There was no correlation between nutritional status during the nestling phase (measured as size-corrected body mass day 14 post-hatch) and antibody responsiveness as an adult. On the other hand, the heritability of responsiveness to diphtheria and tetanus, as estimated by parent-offspring regression, was 0.21+/-0.51 and 1.21+/-0.40 SE, respectively. Thus, while there was little evidence that natural variation in antibody responsiveness to these antigens reflected nutritional conditions during early life, responsiveness to at least one of the antigens (tetanus) had a strong genetic component

Skattning av effekter av jordbrukets markanvändning på jordbruksfåglar med hjälp av "joint species modelling"

This study seeks evidence of benefits to farmland birds of reversing land use intensification on and among arable fields and to what extent benefits are moderated by presence of more natural habitats (semi-natural pastures and field borders). The study compares bird numbers for a set of farmland bird species in landscapes/sites differing in agricultural land use and amount of semi-natural habitats. The dataset is comprised of bird counts and agricultural habitat characteristics from a set of 1km radius circular landscapes distributed in the most to medium productive regions in Scania (southern-most province of Sweden). Study sites (landscapes) where selected to maximise orthogonality in the habitat characteristics. Bird counts in each landscape where made for 5 min. at 11 – 16 points distributed in a 4 by 4 grid (approx. 400 m between points; half the points, “columns” 1 and 3, where moved to nearest field border; points more than 50 m outside farmland where discarded; points that could not be accessed (gardens etc.) where moved to nearest access point). Landscapes were visited twice (>= 1 week in between) during the period 2011-05-11 – 2011-06-14. Only counts of a set of farmland birds is included in the dataset (see metadata). All birds seen or heard within 150 m were counted. Habitat characteristics were extracted from the IACS database (Blockdatabasen) maintained by the Swedish Board of Agriculture for administration of subsidies. Full description of design and methods can be found in Stjernman et al. Ecological Applications 2019 (In press). The paper (Stjernman et al Ecological Applications 2019, currently In Press) and dataset are to be cited when using the dataset.I den här studien undersöker vi förhållandet mellan fågelförekomst och intensitet i markanvändning i ett antal landskap (1km radie) belägna i Skånes slätt- och mellanbygd. I upp till 16 punkter (ca 400 m emellan varje) räknades vid två tillfällen alla fåglar tillhörande ett urval arter som betraktas beroende av jordbruksmark. Alla individer inom 150 m från observationspunkten sedda inom 5 min inkluderades. Markanvändningsinformation för landskapen hämtades från Jordbruksverkets Blockdatabas. Utförligare information om variabler i data finns i metadata och vidare finns metoder och data utförligare beskrivna i Stjernman et al. Ecological Applications (In press). Artikeln (Stjernman et al Ecological Applications 2019, In Press) och dataset citeras vid användning av data

Long-term effects of nestling condition on blood parasite resistance in blue tits (Cyanistes caeruleus).

Little is know about whether the conditions experienced during ontogeny affect resistance to parasites later in life in wild animals. Here, we used a population of blue tits (Cyanistes caeruleus (L., 1758)) to investigate to what extent conditions experienced during the nestling stage could explain the ability to control blood parasite (Haemoproteus majoris (Laveran, 1902)) infections 1 year later. Although short-term effects may be expected based on the well-known sensitivity of the immune system to current conditions, it is less known whether this translates into a permanent alteration of parasite resistance. By relating nestling condition (measured as body mass or size-corrected body mass) at the beginning and end of the nestling stage to parasite intensity of individual recruiting birds 1 year later, we indeed found significant positive effects of both early and late nestling condition on the long-term ability to control parasites. These results indicate that parasites may be important as a mechanistic explanation for the trade-off between number and quality of offspring. It further points to the potential relevance for maternal effects in host–parasite interactions