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  • 1.
    Bergvall, Ulrika Alm
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Leimar, Olof
    Stockholm University, Faculty of Science, Department of Zoology.
    Plant secondary compounds and the frequency of food types affect food choice by mammalian herbivores2005In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 86, no 9, p. 2450-2460Article in journal (Refereed)
    Abstract [en]

    We have investigated food choice in individual fallow deer (Dama dama) encountering different relative frequencies of food types in the form of bowls containing pellets with either high or low concentrations of hydrolyzable tannin. We performed two similar experiments, one with large and one with small differences in tannic acid concentration. With small differences in tannic acid concentration, the ratio of the consumption per low- and high-tannin bowl was independent of frequency of occurrence, but with large differences in tannic acid concentration, we found frequency-dependent food choice. The deer ate proportionally less from high-tannin bowls if these occurred at low relative frequency. Variation between frequency treatments in the average order of encounter of bowl types might have produced this effect, because we found that the deer left a high-tannin bowl more quickly if they had switched to it from a low-tannin bowl. We argue that the perceived contrast between the tastes of different food types can play a role for food choice by mammalian herbivores.

  • 2. Dahlgren, Johan P.
    et al.
    Bengtsson, Karin
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The demography of climate-driven and density-regulated population dynamics in a perennial plant2016In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 4, p. 899-907Article in journal (Refereed)
    Abstract [en]

    Identifying the internal and external drivers of population dynamics is a key objective in ecology, currently accentuated by the need to forecast the effects of climate change on species distributions and abundances. The interplay between environmental and density effects is one particularly important aspect of such forecasts. We examined the simultaneous impact of climate and intraspecific density on vital rates of the dwarf shrub Fumana procumbens over 20 yr, using generalized additive mixed models. We then analyzed effects on population dynamics using integral projection models. The population projection models accurately captured observed fluctuations in population size. Our analyses suggested the population was intrinsically regulated but with annual fluctuations in response to variation in weather. Simulations showed that implicitly assuming variation in demographic rates to be driven solely by the environment can overestimate extinction risks if there is density dependence. We conclude that density regulation can dampen effects of climate change on Fumana population size, and discuss the need to quantify density dependence in predictions of population responses to environmental changes.

  • 3.
    Dahlgren, Johan P.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Garcia, Maria B.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Nonlinear relationships between vital rates and state variables in demographic models2011In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 92, no 5, p. 1181-1187Article in journal (Refereed)
    Abstract [en]

    To accurately estimate population dynamics and viability, structured population models account for among-individual differences in demographic parameters that are related to individual state. In the widely used matrix models, such differences are incorporated in terms of discrete state categories, whereas integral projection models (IPMs) use continuous state variables to avoid artificial classes. In IPMs, and sometimes also in matrix models, parameterization is based on regressions that do not always model nonlinear relationships between demographic parameters and state variables. We stress the importance of testing for nonlinearity and propose using restricted cubic splines in order to allow for a wide variety of relationships in regressions and demographic models. For the plant Borderea pyrenaica, we found that vital rate relationships with size and age were nonlinear and that the parameterization method had large effects on predicted population growth rates, lambda (linear IPM, 0.95; nonlinear IPMs, 1.00; matrix model, 0.96). Our results suggest that restricted cubic spline models are more reliable than linear or polynomial models. Because even weak nonlinearity in relationships between vital rates and state variables can have large effects on model predictions, we suggest that restricted cubic regression splines should be considered for parameterizing models of population dynamics whenever linearity cannot be assumed.

  • 4.
    Donadi, Serena
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden; University of Groningen, The Netherlands.
    Nilsson Austin, Åsa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Svartgren, Evira
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson, Britas Klemens
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Hansen, J. P.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Density-dependent positive feedbacks buffer aquatic plants from interactive effects of eutrophication and predator loss2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 11, p. 2515-2524Article in journal (Refereed)
    Abstract [en]

    Self-facilitation allows populations to persist under disturbance by ameliorating experienced stress. In coastal ecosystems, eutrophication and declines of large predatory fish are two common disturbances that can synergistically impact habitat-forming plants by benefitting ephemeral algae. In theory, density-dependent intraspecific plant facilitation could weaken such effects by ameliorating the amount of experienced stress. Here, we tested whether and how shoot density of a common aquatic plant (Myriophyllum spicatum) alters the response of individual plants to eutrophication and exclusion of large predatory fish, using a 12-week cage experiment in the field. Results showed that high plant density benefitted individual plant performance, but only when the two stressors were combined. Epiphytic algal biomass per plant more than doubled in cages that excluded large predatory fish, indicative of a trophic cascade. Moreover, in this treatment, individual shoot biomass, as well as number of branches, increased with density when nutrients were added, but decreased with density at ambient nutrient levels. In contrast, in open cages that large predatory fish could access, epiphytic algal biomass was low and individual plant biomass and number of branches were unaffected by plant density and eutrophication. Plant performance generally decreased under fertilization, suggesting stressful conditions. Together, these results suggest that intraspecific plant facilitation occurred only when large fish exclusion (causing high epiphyte load) was accompanied by fertilization, and that intraspecific competition instead prevailed when no nutrients were added. As coastal ecosystems are increasingly exposed to multiple and often interacting stressors such as eutrophication and declines of large predatory fish, maintaining high plant density is important for ecosystem-based management.

  • 5. Donadi, Serena
    et al.
    van der Heide, Tjisse
    van der Zee, Els M.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Systems Ecology. University of Gothenburg, Sweden; University of Groningen, The Netherlands.
    van de Koppel, Johan
    Weerman, Ellen J.
    Piersma, Theunis
    Olff, Han
    Eriksson, Britas Klemens
    Cross-habitat interactions among bivalve species control community structure on intertidal flats2013In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 94, no 2, p. 489-498Article in journal (Refereed)
    Abstract [en]

    Increasing evidence shows that spatial interactions between sedentary organisms can structure communities and promote landscape complexity in many ecosystems. Here we tested the hypothesis that reef-forming mussels (Mytilus edulis L.), a dominant intertidal ecosystem engineer in the Wadden Sea, promote abundances of the burrowing bivalve Cerastoderma edule L. (cockle) in neighboring habitats at relatively long distances coastward from mussel beds. Field surveys within and around three mussel beds showed a peak in cockle densities at 50-100 m toward the coast from the mussel bed, while cockle abundances elsewhere in the study area were very low. Field transplantation of cockles showed higher survival of young cockles (2-3 years old) and increased spat fall coastward of the mussel bed compared to within the bed and to areas without mussels, whereas growth decreased within and coastward of the mussel bed. Our measurements suggest that the observed spatial patterns in cockle numbers resulted from (1) inhibition effects by the mussels close to the beds due to preemptive algal depletion and deteriorated sediment conditions and (2) facilitation effects by the mussels farther away from the beds due to reduction of wave energy. Our results imply that these spatial, scale-dependent interactions between reef-forming ecosystem engineers and surrounding communities of sedentary benthic organisms can be an important determinant of the large-scale community structure in intertidal ecosystems. Understanding this interplay between neighboring communities of sedentary species is therefore essential for effective conservation and restoration of soft-bottom intertidal communities.

  • 6.
    Dynesius, Mats
    et al.
    Umeå University.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    Nilsson, Christer
    Umeå University.
    High resilience in stream-side bryophyte assemblages in boreal forests2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, p. 1042-1054Article in journal (Refereed)
  • 7.
    Ehrlén, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Raabova, Jana
    Dahlgren, Johan P.
    Flowering schedule in a perennial plant; life-history trade-offs, seed predation, and total offspring fitness2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 8, p. 2280-2288Article in journal (Refereed)
    Abstract [en]

    Optimal timing of reproduction within a season may be influenced by several abiotic and biotic factors. These factors sometimes affect different components of fitness, making assessments of net selection difficult. We used estimates of offspring fitness to examine how pre-dispersal seed predation influences selection on flowering schedule in an herb with a bimodal flowering pattern, Actaea spicata. Within individuals, seeds from flowers on early terminal inflorescences had a higher germination rate and produced larger seedlings than seeds from flowers on late basal inflorescences. Reproductive value, estimated using demographic integral projection models and accounting for size-dependent differences in future performance, was two times higher for intact seeds from early flowers than for seeds from late flowers. Fruits from late flowers were, however, much more likely to escape seed predation than fruits from early flowers. Reproductive values of early and late flowers balanced at a predation intensity of 63%. Across 15 natural populations, the strength of selection for allocation to late flowers was positively correlated with mean seed predation intensity. Our results suggest that the optimal shape of the flowering schedule, in terms of the allocation between early and late flowers, is determined by the trade-off between offspring number and quality, and that variation in antagonistic interactions among populations influences the balancing of this trade-off. At the same time they illustrate that phenotypic selection analyses that fail to account for differences in offspring fitness might be misleading.

  • 8. Ekholm, Adam
    et al.
    Roslin, Tomas
    Pulkkinen, Pertti
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dispersal, host genotype and environment shape the spatial dynamics of a parasite in the wild2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 10, p. 2574-2584Article in journal (Refereed)
    Abstract [en]

    Dispersal, environment and genetic variation may all play a role in shaping host-parasite dynamics. Yet, in natural systems, their relative importance remains unresolved. Here, we do so for the epidemiology of a specialist parasite (Erysiphe alphitoides) on the pedunculate oak (Quercus robur). For this purpose, we combine evidence from a multi-year field survey and two dispersal experiments, all conducted at the landscape scale. Patterns detected in the field survey suggest that the parasite is structured as a metapopulation, with trees in denser oak stands characterized by higher parasite occupancy, higher colonization rates and lower extinction rates. The dispersal experiments revealed a major impact of the environment and of host genotype on the presence and abundance of the parasite, with a weaker but detectable imprint of dispersal limitation. Overall, our findings emphasize that dispersal, host genotype and the environment jointly shape the spatial dynamics of a parasite in the wild.

  • 9. Emerson, Brent C.
    et al.
    Kolm, Niclas
    Uppsala universitet, Zooekologi.
    Species diversity can drive speciation: reply2007In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 88, no 8, p. 2135-2138Article in journal (Refereed)
  • 10. Fernandez-Conradi, Pilar
    et al.
    Jactel, Hervé
    Robin, Cécile
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Castagneyrol, Bastien
    Fungi reduce preference and performance of insect herbivores on challenged plants2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 2, p. 300-311Article in journal (Refereed)
    Abstract [en]

    Although insect herbivores and fungal pathogens frequently share the same individual host plant, we lack general insights in how fungal infection affects insect preference and performance. We addressed this question in a meta-analysis of 1,113 case studies gathered from 101 primary papers that compared preference or performance of insect herbivores on control vs. fungus challenged plants. Generally, insects preferred, and performed better on, not challenged plants, regardless of experimental conditions. Insect response to fungus infection significantly differed according to fungus lifestyle, insect feeding guild, and the spatial scale of the interaction (local/distant). Insect performance was reduced on plants challenged by biotrophic pathogens or endophytes but not by necrotrophic pathogens. For both chewing and piercing-sucking insects, performance was reduced on challenged plants when interactions occurred locally but not distantly. In plants challenged by biotrophic pathogens, both preference and performance of herbivores were negatively impacted, whereas infection by necrotrophic pathogens reduced herbivore preference more than performance and endophyte infection reduced only herbivore performance. Our study demonstrates that fungi could be important but hitherto overlooked drivers of plant-herbivore interactions, suggesting both direct and plant-mediated effects of fungi on insect's behavior and development.

  • 11.
    Fogelström, Elsa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Olofsson, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Posledovich, Diana
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Dahlgren, Johan P.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Plant-herbivore synchrony and selection on plant flowering phenology2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 3, p. 703-711Article in journal (Refereed)
    Abstract [en]

    Temporal variation in natural selection has profound effects on the evolutionary trajectories of populations. One potential source of variation in selection is that differences in thermal reaction norms and temperature influence the relative phenology of interacting species. We manipulated the phenology of the butterfly herbivore Anthocharis cardamines relative to genetically identical populations of its host plant, Cardamine pratensis, and examined the effects on butterfly preferences and selection acting on the host plant. We found that butterflies preferred plants at an intermediate flowering stage, regardless of the timing of butterfly flight relative to flowering onset of the population. Consequently, the probability that plant genotypes differing in timing of flowering should experience a butterfly attack depended strongly on relative phenology. These results suggest that differences in spring temperature influence the direction of herbivore-mediated selection on flowering phenology, and that climatic conditions can influence natural selection also when phenotypic preferences remain constant.

  • 12. Fortunel, Claire
    et al.
    Garnier, Eric
    Joffre, R
    Kazakou, E
    Quested, Helen
    Stockholm University, Faculty of Science, Department of Botany.
    Grigulis,
    Lavorel, S
    Ansquer, P
    Castro, H
    Cruz, P
    Dolezal, J
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Freitas, H
    Golodets, C
    Jouany, C
    Kigel, J
    Kleyer, M
    Lehsten, V
    Leps, J
    Meier, T
    Pakeman, R
    Papadimitriou, M
    Papanastasis, V P
    Quétier, F
    Robson, M
    Sternberg, M
    Theau, J-P
    Thébault, A
    Zarovali, M
    Leaf traits capture the effects of land use changes and climate on litter decomposability of grasslands across Europe2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, p. 598-611Article in journal (Refereed)
  • 13.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Host plant induced larval decision-making in a habitat/host plant generalist butterfly2010In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 91, p. 15-21Article in journal (Refereed)
    Abstract [en]

    Phenotypic plasticity can be a passive response to fluctuating environmental conditions or an active and presumably adaptive (evolved) response selected for in different environments. Here we ask if the larval decision to enter diapause when reared on a host plant associated with a colder habitat is an active or a passive response to host plant quality or suitability. We compare plasticity in larval propensity to enter diapause of the habitat generalist butterfly Leptidea sinapis and the meadow specialist Leptidea reali in a range of temperatures and long daylength on a forest plant, Lathyrus linifolius, and a meadow-associated plant, Lathyrus pratensis. The warmer meadow habitat promotes direct development whereas the colder forest habitat is conducive to diapause. Larvae of L. sinapis had a higher propensity to enter diapause when reared on the forest plant L. linifolius across all temperatures. Conversely, the propensity of L. reali to enter diapause was consistently lower and did not differ between host plants. Larval growth rates were similar between and within butterfly species and between host plants. Hence, we conclude that larval pathway decision-making in L. sinapis is an active response mediated by information from their host plants.

  • 14.
    Hambäck, Peter A.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Inouye, Brian D.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Florida State University, Tallahassee, USA.
    Andersson, Petter
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Underwood, Nora
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Florida State University, Tallahassee, USA.
    Effects of plant neighborhoods on plant-herbivore interactions: resource dilution and associational effects2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 5, p. 1370-1383Article in journal (Refereed)
    Abstract [en]

    Effects of neighboring plants on herbivore damage to a focal plant (associational effects) have been documented in many systems and can lead to either increased or decreased herbivore attack. Mechanistic models that explain the observed variety of herbivore responses to local plant community composition have, however, been lacking. We present a model of herbivore responses to patches that consist of two plant types, where herbivore densities on a focal plant are determined by a combination of patch-finding, within-patch redistribution, and patch-leaving. Our analyses show that the effect of plant neighborhood on herbivores depends both on how plant and herbivore traits combine to affect herbivore movement and on how experimental designs reveal the effects of plant density and plant relative frequency. Associational susceptibility should be the dominant pattern when herbivores have biased landing rates within patches. Other behavioral decision rules lead to mixed responses, but a common pattern is that in mixed patches, one plant type experiences associational resistance while the other plant experiences associational susceptibility. In some cases, the associational effect may shift sign along a gradient of plant frequency, suggesting that future empirical studies should include more than two plant frequencies to detect nonlinearities. Finally, we find that associational susceptibility should be commonly observed in experiments using replacement designs, whereas associational resistance will be the dominant pattern when using additive designs. Consequently, outcomes from one experimental design cannot be directly compared to studies with other designs. Our model can also be translated to other systems with foragers searching for multiple resource types.

  • 15. Homyak, P. M.
    et al.
    Blankinship, J. C.
    Slessarev, E.
    Schaeffer, S. M.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Schimel, J. P.
    Effects of altered dry-season length and plant inputs on soluble soil carbon2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 10, p. 2348-2362Article in journal (Refereed)
    Abstract [en]

    Soil moisture controls microbial activity and soil carbon cycling. Because microbial activity decreases as soils dry, decomposition of soil organic matter (SOM) is thought to decrease with increasing drought length. Yet, microbial biomass and a pool of water‐extractable organic carbon (WEOC) can increase as soils dry, perhaps implying microbes may continue to break down SOM even if drought stressed. Here, we test the hypothesis that WEOC increases as soils dry because exoenzymes continue to break down litter, while their products accumulate because they cannot diffuse to microbes. To test this hypothesis, we manipulated field plots by cutting off litter inputs and by irrigating and excluding precipitation inputs to extend or shorten the length of the dry season. We expected that the longer the soils would remain dry, the more WEOC would accumulate in the presence of litter, whereas shortening the length of the dry season, or cutting off litter inputs, would reduce WEOC accumulation. Lastly, we incubated grass roots in the laboratory and measured the concentration of reducing sugars and potential hydrolytic enzyme activities, strictly to understand the mechanisms whereby exoenzymes break down litter over the dry season. As expected, extending dry season length increased WEOC concentrations by 30% above the 108 μg C/g measured in untreated plots, whereas keeping soils moist prevented WEOC from accumulating. Contrary to our hypothesis, excluding plant litter inputs actually increased WEOC concentrations by 40% above the 105 μg C/g measured in plots with plants. Reducing sugars did not accumulate in dry senesced roots in our laboratory incubation. Potential rates of reducing sugar production by hydrolytic enzymes ranged from 0.7 to 10 μmol·g−1·h−1 and far exceeded the rates of reducing sugar accumulation (~0.001 μmol·g−1·h−1). Our observations do not support the hypothesis that exoenzymes continue to break down litter to produce WEOC in dry soils. Instead, we develop the argument that physical processes are more likely to govern short‐term WEOC dynamics via slaking of microaggregates that stabilize SOM and through WEOC redistribution when soils wet up, as well as through less understood effects of drought on the soil mineral matrix.

  • 16.
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Botany.
    No increase in colonization rate of boreal bryophytes close to propagule sources2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, p. 160-169Article in journal (Refereed)
  • 17. Jose Bullejos, Francisco
    et al.
    Carrillo, Presentacion
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Manuel Medina-Sanchez, Juan
    Gabriel Balseiro, Esteban
    Villar-Argaiz, Manuel
    Shifts in food quality for herbivorous consumer growth: multiple golden means in the life history2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 5, p. 1272-1284Article in journal (Refereed)
    Abstract [en]

    Consumer growth can be affected by imbalances between the nutrient content of the consumer and its food resource. Although ontogenetic-driven changes in animal composition are well documented, their potential consequences for the organism's sensitivity to food quality constraints have remained elusive. Here we show that the potential growth response of the copepod Mixodiaptomus laciniatus (as %RNA and RNA:DNA ratio) to the natural gradient of seston carbon (C):nutrient ratio is unimodal and stage specific. Solution of the equation given by the first derivative function provided the optimum C:nutrient ratio for maximum stage-specific growth, which increased during ontogeny. The peakedness of the function indicated that animal vulnerability to suboptimal food quality decreased as juveniles reached adulthood. Consistent with these results, a field experiment demonstrated that potential consumer growth responded to variations in seston C:phosphorus ratio, and that early life stages were particularly vulnerable to suboptimal food quality.

  • 18.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nascimento, Francisco J. A.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Higher diversity of deposit-feeding macrofauna enhances phytodetritus processing2010In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 91, no 5, p. 1414-1423Article in journal (Refereed)
    Abstract [en]

    The link between biodiversity and ecosystem functioning is an important question that remains unresolved, particularly in marine systems, in which cycling of organic matter by benthic organisms is of global significance. Direct observations of specific resource use by each species in single- and multispecies communities, as quantified by stable isotopes, facilitates a mechanistic understanding of the importance of each species for ecosystem functioning. We tested the effects of altered biodiversity (species richness) of deposit-feeding macrofauna on incorporation and burial of phytodetritus in combinations of three species representing natural communities found in the sediments of the species-poor Baltic Sea. The three species, two amphipods and a bivalve, had different rates of incorporation and burial and different needs for carbon (C) and nitrogen (N). The amphipods exhibited clear resource partitioning in sympatry, as a result of vertical separation in the sediment and consequent differential use of food. Communities of several species incorporated more C and N than expected from the respective single-species treatments, due to higher incorporation by surface feeders in multispecies treatments. Community incorporation of N in the most diverse treatment even exceeded N incorporation by a single-species treatment of the best-performing species, showing transgressive over-yielding. This over-yielding was primarily due to positive complementarity in all treatments. Diverse soft bottoms are also likely to be more productive in the long run, as species-specific traits (subsurface feeding) preserve fresh phytodetritus by burying it to depths in the sediment at which the mineralization rate is low. The more diverse sediment communities showed more efficient trophic transfer of phytodetritus, a finding of general significance for understanding biological processes driving the transformation of nutrients and energy in benthic ecosystems.

  • 19.
    Knape, Jonas
    et al.
    Lund University, Department of Theoretical Ecology.
    Jonzén, Niclas
    Lund University, Department of Theoretical Ecology.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Kikkawa, Jiro
    McCallum, Hamish
    Individual heterogeneity and senescence in Silvereyes on Heron Island2011In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 92, no 4, p. 813-820Article in journal (Refereed)
    Abstract [en]

    Individual heterogeneity and correlations between life history traits play a fundamental role in life history evolution and population dynamics. Unobserved individual heterogeneity in survival can be a nuisance for estimation of age effects at the individual level by causing bias due to mortality selection. We jointly analyze survival and breeding output from successful breeding attempts in an island population of Silvereyes (Zosterops lateralis chlorocephalus) by fitting models that incorporate age effects and individual heterogeneity via random effects. The number of offspring produced increased with age of parents in their first years of life but then eventually declined with age. A similar pattern was found for the probability of successful breeding. Annual survival declined with age even when individual heterogeneity was not accounted for. The rate of senescence in survival, however, depends on the variance of individual heterogeneity and vice versa; hence, both cannot be simultaneously estimated with precision. Model selection supported individual heterogeneity in breeding performance, but we found no correlation between individual heterogeneity in survival and breeding performance. We argue that individual random effects, unless unambiguously identified, should be treated as statistical nuisance or taken as a starting point in a search for mechanisms rather than given direct biological interpretation.

  • 20. Kolb, Annette
    et al.
    Dahlgren, Johan P.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Population size affects vital rates but not population growth rate of a perennial plant2010In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 91, no 11, p. 3210-3217Article in journal (Refereed)
    Abstract [en]

    Negative effects of habitat fragmentation on individual performance have been widely documented, but relatively little is known about how simultaneous effects on multiple vital rates translate into effects on population viability in long-lived species. In this study, we examined relationships between population size, individual growth, survival and reproduction, and population growth rate in the perennial plant Phyteuma spicatum. Population size positively affected the growth of seedlings, the survival of juveniles, the proportion of adults flowering, and potential seed production. Analyses with integral projection models, however, showed no relationship between population size and population growth rate. This was due to the fact that herbivores and pathogens eliminated the relationship between population size and seed production, and that population growth rate was not sensitive to changes in the vital rates that varied with population size. We conclude that effects of population size on vital rates must not translate into effects on population growth rate, and that populations of long-lived organisms may partly be able to buffer negative effects of small population size on vital rates that have a relatively small influence on population growth rate. Our study illustrates that we need to be cautious when assessing the consequences of habitat fragmentation for population viability based on effects on only one or a few vital rates.

  • 21.
    Lindborg, Regina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Historical landscape connectivity affects present plant species diversity2004In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 85, no 7, p. 1840-1845Article in journal (Refereed)
    Abstract [en]

    Transformation of landscapes is considered to be one of the main drivers behind species loss, regionally and globally. Theory and empirical studies suggest that landscape structure influences species diversity in many habitats. These effects may be manifested at different spatial scales depending on species response to landscape heterogeneity. A similar, but often neglected, scaling issue concerns the temporal scale of species response to landscape change. In this study, we found time lags of 50-100 years in the response of plant species diversity to changing configuration of habitats in the landscape. When analyzing remnants of traditionally managed seminatural grasslands in Sweden, we found that species diversity was not related to present-day connectivity of the investigated sites, irrespective of spatial scale (3.1-12.5 km(2)). However, when using maps depicting landscapes 50 and 100 years ago, respectively, strong positive effects of habitat connectivity appeared, at increasing spatial scale for the older landscapes. Thus, analyses of how species diversity relates to present-day landscapes may be misleading, and future species loss may be expected even if the present landscape is maint.

  • 22.
    Lindestad, Olle
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Local adaptation of photoperiodic plasticity maintains life cycle variation within latitudes in a butterfly2019In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 100, no 1, article id e02550Article in journal (Refereed)
    Abstract [en]

    The seasonal cycle varies geographically and organisms are under selection to express life cycles that optimally exploit their spatiotemporal habitats. In insects, this often means producing an annual number of generations (voltinism) appropriate to the local season length. Variation in voltinism may arise from variation in environmental factors (e.g., temperature or photoperiod) acting on a single reaction norm shared across populations, but it may also result from local adaptation of reaction norms. However, such local adaptation is poorly explored at short geographic distances, especially within latitudes. Using a combination of common-garden rearing and life cycle modeling, we have investigated the causal factors behind voltinism variation in Swedish populations of the butterfly Pararge aegeria, focusing on a set of populations that lie within a single degree of latitude but nonetheless differ in season length and voltinism. Despite considerable differences in ambient temperature between populations, modeling suggested that the key determinant of local voltinism was in fact interpopulation differences in photoperiodic response. These include differences in the induction thresholds for winter diapause, as well as differences in photoperiodic regulation of larval development, a widespread but poorly studied phenomenon. Our results demonstrate previously neglected ways that photoperiodism may mediate insect phenological responses to temperature, and emphasize the importance of local adaptation in shaping phenological patterns in general, as well as for predicting the responses of populations to changes in climate.

  • 23. Nash, Kirsty L.
    et al.
    Allen, Craig R.
    Angeler, David G.
    Barichievy, Chris
    Eason, Tarsha
    Garmestani, Ahjond S.
    Graham, Nicholas A. J.
    Granholm, Dean
    Knutson, Melinda
    Nelson, R. John
    Nyström, Magnus
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Stow, Craig A.
    Sundström, Shana M.
    Discontinuities, cross-scale patterns, and the organization of ecosystems2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 3, p. 654-667Article in journal (Refereed)
    Abstract [en]

    Ecological structures and processes occur at specific spatiotemporal scales, and interactions that occur across multiple scales mediate scale-specific (e.g., individual, community, local, or regional) responses to disturbance. Despite the importance of scale, explicitly incorporating a multi-scale perspective into research and management actions remains a challenge. The discontinuity hypothesis provides a fertile avenue for addressing this problem by linking measureable proxies to inherent scales of structure within ecosystems. Here we outline the conceptual framework underlying discontinuities and review the evidence supporting the discontinuity hypothesis in ecological systems. Next we explore the utility of this approach for understanding cross-scale patterns and the organization of ecosystems by describing recent advances for examining nonlinear responses to disturbance and phenomena such as extinctions, invasions, and resilience. To stimulate new research, we present methods for performing discontinuity analysis, detail outstanding knowledge gaps, and discuss potential approaches for addressing these gaps.

  • 24. Peery, M. Zachariah
    et al.
    Beissinger, Steven R.
    House, Roger F.
    Berube, Martine
    Hall, Laurie A.
    Sellas, Anna
    Palsböll, Per J.
    Stockholm University, Faculty of Science, Department of Genetics, Microbiology and Toxicology.
    Characterizing source-sink dynamics with genetic parentage assignments2008In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 89, no 10, p. 2746-2759Article in journal (Refereed)
    Abstract [en]

    Source-sink dynamics have been suggested to characterize the population structure of many species, but the prevalence of source-sink systems in nature is uncertain because of inherent challenges in estimating migration rates among populations. Migration rates are often difficult to estimate directly with demographic methods, and indirect genetic methods are subject to a variety of assumptions that are difficult to meet or to apply to evolutionary timescales. Furthermore, such methods cannot be rigorously applied to high-gene-flow species. Here, we employ genetic parentage assignments in conjunction with demographic simulations to infer the level of immigration into a putative sink population. We use individual-based demographic models to estimate expected distributions of parent offspring dyads under competing sink and closed-population models. By comparing the actual number of parent-offspring dyads (identified from multilocus genetic profiles) in a random sample of individuals taken from a population to expectations under these two contrasting demographic models, it is possible to estimate the rate of immigration and test hypotheses related to the role of immigration on population processes on an ecological timescale. The difference in the expected number of parent-offspring dyads between the two population models was greatest when immigration into the sink population was high, indicating that unlike traditional population genetic inference models, the highest degree of statistical power is achieved for the approach presented here when migration rates are high. We used the proposed genetic parentage approach to demonstrate that a threatened population of Marbled Murrelets (Brachyramphus marmotus) appears to be supplemented by a low level of immigration (similar to 2-6% annually) from other populations.

  • 25. Reynolds, Pamela L.
    et al.
    Stachowicz, John J.
    Hovel, Kevin
    Boström, Christoffer
    Boyer, Katharyn
    Cusson, Mathieu
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Engel, Friederike G.
    Engelen, Aschwin H.
    Eriksson, Britas Klemens
    Fodrie, F. Joel
    Griffin, John N.
    Hereu, Clara M.
    Hori, Masakazu
    Hanley, Torrance C.
    Ivanov, Mikhail
    Jorgensen, Pablo
    Kruschel, Claudia
    Lee, Kun-Seop
    McGlathery, Karen
    Moksnes, Per-Olav
    Nakaoka, Masahiro
    O'Connor, Mary I.
    O'Connor, Nessa E.
    Orth, Robert J.
    Rossi, Francesca
    Ruesink, Jennifer
    Sotka, Erik E.
    Thormar, Jonas
    Tomas, Fiona
    Unsworth, Richard K. F.
    Whalen, Matthew A.
    Duffy, J. Emmett
    Latitude, temperature, and habitat complexity predict predation pressure in eelgrass beds across the Northern Hemisphere2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 1, p. 29-35Article in journal (Refereed)
    Abstract [en]

    Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37 degrees of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas insitu water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions.

  • 26. Thomann, Michel
    et al.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ågren, Jon
    Grazers affect selection on inflorescence height both directly and indirectly and effects change over time2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 10, p. 2167-2175Article in journal (Refereed)
    Abstract [en]

    Selection mediated by one biotic agent will often be modified by the presence of other biotic interactions, and the importance of such indirect effects might change over time. We conducted an 11-yr field experiment to test the prediction that large grazers affect selection on floral display of the dimorphic herb Primula farinosa not only directly through differential grazing damage, but also indirectly by affecting vegetation height and thereby selection mediated by pollinators and seed predators. Exclusion of large grazers increased vegetation height and the strength of pollinator-mediated selection for tall inflorescences and seed-predator-mediated selection for short inflorescences. The direct effect of grazers on selection resulting from differential grazing damage to the two scape morphs showed no temporal trend. By contrast, the increase in vegetation height in exclosures over time was associated with an increase in selection mediated by pollinators and seed predators. In the early years of the experiment, the indirect effects of grazers on selection mediated by pollinators and seed predators were weak, whereas at the end of the experiment, the indirect effects were of similar magnitude as the direct effect due to differential grazing damage. The results demonstrate that the indirect effects of a selective agent can be as strong as its direct effects, and that the relative importance of direct vs. indirect effects on selection can change over time. A full understanding of the ecological processes governing variation in selection thus requires that both direct and indirect effects of biotic interactions are assessed.

  • 27.
    Valdés, Alicia
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Caterpillar seed predators mediate shifts in selection on flowering phenology in their host plant2017In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 98, no 1, p. 228-238Article in journal (Refereed)
    Abstract [en]

    Variation in selection among populations and years has important implications for evolutionary trajectories of populations. Yet, the agents of selection causing this variation have rarely been identified. Selection on the time of reproduction within a season in plants might differ both among populations and among years, and selection can be mediated by both mutualists and antagonists. We investigated if differences in the direction of phenotypic selection on flowering phenology among 20 populations of Gentiana pneumonanthe during 2 yr were related to the presence of the butterfly seed predator Phengaris alcon, and if butterfly incidence was associated with the abundance of the butterfly's second host, Myrmica ants. In plant populations without the butterfly, phenotypic selection favored earlier flowering. In populations where the butterfly was present, caterpillars preferentially attacked early-flowering individuals, shifting the direction of selection to favoring later flowering. Butterfly incidence in plant populations increased with ant abundance. Our results demonstrate that antagonistic interactions can shift the direction of selection on flowering phenology, and suggest that such shifts might be associated with differences in the community context.

  • 28. Virta, Leena
    et al.
    Gammal, Hanna
    Järnström, Marie
    Bernard, Guillaume
    Soininen, Janne
    Norkko, Joanna
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    The diversity of benthic diatoms affects ecosystem productivity in heterogeneous coastal environments2019In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 100, no 9, article id e02765Article in journal (Refereed)
    Abstract [en]

    The current decrease in biodiversity affects all ecosystems, and the impacts of diversity on ecosystem functioning need to be resolved. So far, marine studies about diversity-ecosystem productivity-relationships have concentrated on small-scale, controlled experiments, with often limited relevance to natural ecosystems. Here, we provide a real-world study on the effects of microorganismal diversity (measured as the diversity of benthic diatom communities) on ecosystem productivity (using chlorophyll a concentration as a surrogate) in a heterogeneous marine coastal archipelago. We collected 78 sediment cores at 17 sites in the northern Baltic Sea and found exceptionally high diatom diversity (328 observed species). We used structural equation models and quantile regression to explore relationships between diatom diversity and productivity. Previous studies have found contradictory results in the relationship between microorganismal diversity and ecosystem productivity, but we showed a linear and positive basal relationship between diatom diversity and productivity, which indicates that diatom diversity most likely forms the lowest boundary for productivity. Thus, although productivity can be high even when diatom diversity is low, high diatom diversity supports high productivity. The trait composition was more effective than taxonomical composition in showing such a relationship, which could be due to niche complementarity. Our results also indicated that environmental heterogeneity leads to substantial patchiness in the diversity of benthic diatom communities, mainly induced by the variation in sediment organic matter content. Therefore, future changes in precipitation and river runoff and associated changes in the quality and quantity of organic matter in the sea, will also affect diatom communities and, hence, ecosystem productivity. Our study suggests that benthic microorganisms are vital for ecosystem productivity, and together with the substantial heterogeneity of coastal ecosystems, they should be considered when evaluating the potential productivity of coastal areas.

  • 29.
    von Euler, Tove
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ågren, Jon
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Environmental context influences both the intensity of seed predation and plant demographic sensitivity to attack2014In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 2, p. 495-504Article in journal (Refereed)
    Abstract [en]

    Variation in mutualistic and antagonistic interactions are important sources of variation in population dynamics and natural selection. Environmental heterogeneity can influence the outcome of interactions by affecting the intensity of interactions, but also by affecting the demography of the populations involved. However, little is known about the relative importance of environmental effects on interaction intensities and demographic sensitivity for variation in population growth rates. We investigated how soil depth, soil moisture, soil nutrient composition, and vegetation height influenced the intensity of seed predation as well as host plant demography and sensitivity to seed predation in the perennial herb Primula farinosa. Intensity of seed predation ranged from 0% to 80% of seeds damaged among the 24 study populations and was related to soil moisture in two of four years. The effect of seed predation on plant population growth rate () ranged from negligible to a reduction in by 0.70. Sensitivity of population growth rate to predation explained as much of the variation in the reductions in population growth rate due to seed predation as did predation intensity. Plant population growth rate in the absence of seed predation and sensitivity to predation were negatively related to soil depth and soil moisture. Both intensity of predation and sensitivity to predation were positively correlated with potential population growth rate and, as a result, there was no significant relationship between predation intensity and realized population growth rate. We conclude that in our study system environmental context influences the effects of seed predation on plant fitness and population dynamics in two important ways: through variation in interaction intensity and through sensitivity to the effects of this interaction. Moreover, our results show that a given abiotic factor can influence population growth rate in different directions through effects on potential growth rate, intensity of biotic interactions, and the sensitivity of population growth rate to interactions.

  • 30.
    Wiklund, Christer
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    The evolutionary ecology of generalization: among-year variation in host plant use and offspring survival in a butterfly2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 12, p. 3406-3417Article in journal (Refereed)
    Abstract [en]

    The majority of phytophagous insects are relatively specialized in their food habits, and specialization in resource use is expected to be favored by selection in most scenarios. Ecological generalization is less common and less well understood, but it should be selected for by (1) rarity of resources, (2) resource inconstancy, or (3) unreliability of resource quality. Here, we test these predictions by studying egg distribution and offspring survival in the orange tip butterfly, Anthocharis cardamines, on different host plants in Sweden over a five-year period. A total of 3800 eggs were laid on 16 of the 18 crucifers available at the field site during the five years. Three main factors explained host plant generalization: (1) a rarity of food resources in which the female encounter rate of individual crucifer plants was low and within-year phenological succession of flowering periods of the different crucifers meant that individual species were suitable for oviposition only within a short time window, which translates to a low effective abundance of individual crucifer species as experienced by females searching for host plants, making specialization on a single crucifer species unprofitable; (2) variation in food resources in which among-year variation in availability of any one host plant species was high; and (3) larval survivorship varied unpredictably among years on all host plants, thereby necessitating a bet-hedging strategy and use of several different host plants. Unpredictable larval survival was caused by variation in plant stand habitat characteristics, which meant that drowning and death from starvation affected different crucifers differently, and by parasitism, which varied by host plant and year. Hence, our findings are in agreement with the theoretical explanation of ecological generalization above, helping to explain why A. cardamines is a generalist throughout its range with respect to genera within the Cruciferae.

  • 31. Zheng, Chaozhi
    et al.
    Ovaskainen, Otso
    Roslin, Tomas
    Tack, Ayco J. M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Beyond metacommunity paradigms: habitat configuration, life history, and movement shape an herbivore community on oak2015In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 96, no 12, p. 3175-3185Article in journal (Refereed)
    Abstract [en]

    Many empirical studies of metacommunities have focused on the classification of observational patterns into four contrasting paradigms characterized by different levels of movement and habitat heterogeneity. However, deeper insight into the underlying local and regional processes may be derived from a combination of long-term observational data and experimental studies. With the aim of exploring forces structuring the insect metacommunity on oak, we fit a hierarchical Bayesian state-space model to data from observations and experiments. The fitted model reveals large variation in species-specific dispersal abilities and basic reproduction numbers, R-0. The residuals from the model show only weak correlations among species, suggesting a lack of strong interspecific interactions. Simulations with model-derived parameter estimates indicate that habitat configuration and species attributes both contribute substantially to structuring insect communities. Overall, our findings demonstrate that community-level variation in movement and life history are key drivers of metacommunity dynamics.

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