bluuebunny/crossref_metadata_2025 huggingface dataset:
Do males matter? The role of males in population dynamics
Authors: J. Rankin Daniel , Kokko Hanna
Published: December 2007

Models of population dynamics generally neglect the presence of males. While this assumption holds under many circumstances, behavioural ecology increasingly tells us that the presence (or absence) of males may have an impact on female fitness, and hence population sizes. Here we ask the question of whether males matter to population dynamics, operationally defined as a dependency of population growth on the relative density of males. We provide simple models, and evaluate the current empirical evidence for them, that illustrate various mechanisms of such male influence: mate searching behavior, male resource use (including effects of sexual dimorphism), sexual harassment and sexual segregation. In each case, theory predicts that males can have an effect on population densities, and in some extreme cases a positive feedback between an increasingly male‐biased sex ratio and female harassment may theoretically even bring about population extinction. The results of this study, and the literature reviewed, show that the males can have a substantial effect on population dynamics, particularly so when human influences result in biased sex ratios.
The relationship of food intake and ingesta passage predicts feeding ecology in two different megaherbivore groups
Authors: Clauss Marcus , Jürgen Streich W. , Schwarm Angela , Ortmann Sylvia , Hummel Jürgen
Published: December 2007

Digestion, especially of plant material, is a time‐dependent process. In herbivores, an increase in food intake is usually correlated to an acceleration of ingesta passage through the gut, and could hence depress digestive efficiency. Therefore, the nature of the relationship between food intake and ingesta passage (i.e. whether the increase in ingesta passage due to the increase in food intake is mild or drastic) should determine the flexibility of the feeding strategy of herbivore and omnivore species. Using two megaherbivore groups, the elephants and the hippopotamuses, as examples from opposing ends of the range of potential adaptations to this problem, we demonstrate that the species‐specific relationship of food intake and ingesta passage can precisely predict feeding ecology and activity budgets. In hippos, the distinct acceleration in ingesta passage due to increased intake limits the additional energy gained from eating more forage, and explains the comparatively low food intake and short feeding times generally observed in these animals. In elephants, increased food intake only leads to a very moderate increase of ingesta passage, thus theoretically allowing to optimize energy gain by eating more, which is in accord with the high food intake and long feeding times observed in these animals. We suggest that the characterization of the intake‐passage relationship in herbi‐ and omnivorous species is of much higher ecological relevance than the determination of a supposedly species‐specific “passage time/mean retention time”.
Defense mechanisms against grazing: a study of trypsin inhibitor responses to simulated grazing in the sedgeCarex bigelowii
Authors: Lindgren Åsa , Klint Johan , Moen Jon
Published: December 2007

Trypsin inhibitors have been suggested to constitute an inducible defense in the sedgeCarex bigelowii, and some former studies suggest that this might be a cause for the cyclic population dynamics in many alpine and arctic small mammals, for example lemmings (Lemmus lemmus). We investigated this further by using a method of simulated grazing (clipping) at different intensities, in three different habitats with varying resource availability, with different harvest times (hours after clipping), and two different stages of ramets (reproductive/vegetative) in a study from the Swedish mountain range. Our results do not indicate thatC. bigelowiihas an inducible defense constituted by an increase in trypsin inhibitor activity (TIA), but rather that the amount of soluble plant proteins (SPP) is lowered in wounded plants. The responses were somewhat different in the three habitats, with ramets growing in the marsh showing the highest ratio of TIA to SPP, due to low amounts of SPP. We did not find any significant effects of harvest time, or of the stage of the ramet that could support the hypothesis of an inducible defense. To conclude, we could not find any evidence for an inducible defense consisting of trypsin inhibitors inCarex bigelowiiramets, but we did find variations in the amount of SPP that may have nutritional consequences for herbivores.
Small mammalian herbivore determines vegetation response to patchy nutrient inputs
Authors: Denyer Joanne L. , Hartley S. E. , John E. A.
Published: December 2007

Nutrient inputs to plant communities are often spatially heterogeneous, for example those deriving from the dung and urine of large grazing animals. The effect of such localised elevation of nutrients on plant growth and composition has been shown to be modified by the grazing of large herbivores. However, there has been little work on interactions between small mammalian herbivores and such patchy nutrient inputs, even though these interactions are potentially of major significance for plant performance and community structure.

We examined the effect of simulated cattle urine deposition on the vegetation structure, above‐ground biomass and species composition of chalk grassland within enriched patches. Short‐term exclosures were used to determine whether a small herbivore (rabbit) would preferentially graze the vegetation in enriched patches and what impact this interaction would have on the performance of plants in such patches. Rabbit grazing pressure determined whether nutrient inputs had a negative or positive effect on plant biomass. Nutrients increased plant biomass in the absence of grazing, but when exposed to grazing, plants in nutrient‐rich patches had more biomass consumed by herbivores than neighbouring plants. Further, nutrients increased the relative palatability of a less preferred forage species (Brachypodium pinnatum), contributing to changes in plant community composition. We conclude that a small herbivore can drive plant responses to patchily distributed nutrients.
Crustacean zooplankton species richness and productivity: to what extent do the conclusions depend upon the choice of metrics?
Authors: Thackeray S. J.
Published: December 2007

The form of the relationship between productivity and diversity is the subject of much debate. In studies that compare among site variations in species richness, the relationship varies with taxonomic grouping, spatial scale, productivity range, predation pressure and community assembly. However, direct measurements of productivity are often lacking, necessitating the use of proxies. Nutrient concentrations and algal biomass have both been used as such productivity metrics in studies of freshwaters, but no studies have compared explicitly the form of the richness–productivity relationship when different proxies are used in the same study. Furthermore, different studies use species richness data collected over different time periods, ranging from a single day to many years. In this study the relationship between crustacean zooplankton species richness and productivity is examined, using four metrics of productivity and three temporal scales. The productivity metrics differed in their ability to statistically explain variations in species richness, with concentrations of soluble reactive phosphorus and chlorophyll a being the most powerful predictors. However, the form of the productivity–richness relationship differed in each case, being linear in the former analysis and quadratic in the latter. Comparison of analyses based on species data from different time periods, revealed that the magnitude of the productivity effect was greatest for long‐term species richness and smallest for the richness determined on a single sampling occasion. The proportion of the total species pool that was present on any one sampling date was itself dependent on productivity. Differences in the definition of both productivity and species richness can cause variability in the form of the relationship between the two. This may then confound comparisons between studies that use different methodologies.
Reconsidering the mechanistic basis of the metabolic theory of ecology
Authors: O'Connor Michael P. , Kemp Stanley J. , Agosta Salvatore J. , Hansen Frank , Sieg Annette E. , Wallace Bryan P. , McNair James N. , Dunham Arthur E.
Published: December 2007

The recently proposed metabolic theory of ecology (MTE) claims to provide a mechanistic explanation for long known allometric relationships between mass and metabolic rate. The MTE postulates that these patterns of allometry are driven by the primary selective constraint of transport of energy and materials. However, recent evidence along several different lines has called into question both the adequacy and the universality of this mechanism. We review the accumulating body of literature on this subject, adding our own concerns and criticisms. In addition to other difficulties, we argue that MTE fails as a mechanistic explanation of mass versus metabolic rate allometries because: 1) circulatory cost minimization is not a tenable criterion for evolutionary optimization, 2) the Boltzmann type relationships on which MTE depends are inadequate descriptors of complex metabolic pathways, and 3) most of the hypotheses advanced by the MTE do not, in fact, depend on the proposed mechanism and therefore cannot be used to test the theory. We conclude that the MTE should be abandoned as a monolithic explanation for allometric patterns, and that a more realistic path toward a better understanding of allometry would be to consider multiple explanatory mechanisms for physiological allometries.
What are 60 warblers worth? Killing in the name of conservation
Authors: Vucetich John A. , Nelson Michael P.
Published: December 2007

Ecological research sometimes entails animal suffering and even animal killing. The ethical appropriateness of animal suffering and killing in conservation research may entail considerations that differ from many other kinds of research. This is true, insomuch as conservation research is specifically motivated by an ethical premise: an appreciation for non‐human life. In striking contrast with other academic fields (e.g. medicine), however, the ethical dimension of conservation research is only rarely discussed. When it is discussed, it tends to be characterized by logical errors. These errors are important because they are general (i.e. both common and with far‐reaching implications), and they are easily made by intelligent people; especially those with no formal training in ethics or logic. Failure to recognize these errors could stymie efforts to increase the ethical quality of ecological research conducted in the name of conservation.

We take advantage of a recently published dialogue concerning the ethical appropriateness of a specific field experiment that entailed killing black‐throated blue warblers,Dendroica caerulescens. Both sides of this debate exemplify the kinds of errors to which we refer. In this paper we briefly review the arguments presented on each side of this debate, highlight their mistakes, and indicate necessary corrections. We argue that: (1) compliance with animal research regulations, while important, inadequately accommodates the ethical aspects of animal research, and (2) individual ecologists ought to understand themselves what does and does not represent sound and valid arguments for ethical decisions. Finally, we discuss how any ecological researcher might begin to apply our analysis to his or her own research.
Density‐dependent dispersal suggests a genetic measure of habitat suitability
Authors: Carr Denis , Bowman Jeff , J. Wilson Paul
Published: December 2007

Recent research shows that density dependence should result in predictable movements between habitats of different suitability, depending on whether population densities are increasing or decreasing. When population densities are increasing, habitats become filled in order of their suitability, resulting in a net flow from high suitability to low suitability. When populations decrease in density, the reverse can happen. These patterns suggest that genetic information can be used to infer habitat suitability since individual‐based genetic assignment tests permit high resolution assessments of migration. We used replicated landscapes to study fishers (Martes pennanti) during a population increase and predicted that there should be a net flow of individuals from areas of shallow to deep snow, since snow depth has previously been linked to fisher fitness. A total of 769 fishers were sampled from 35 different landscapes and profiled at 16 microsatellite loci. From assignment tests, we inferred five genetic populations. By assigning each of the 35 landscapes to one of these five populations, we were able to determine the proportion of immigrants to each. Consistent with our prediction, there was a positive relationship between the proportion of immigrants and snow depth. The best model of fisher habitat suitability was one with both snow depth and the proportion of coniferous forest in landscapes. Our findings suggest that where population trend is known, genetic information can be used to measure habitat suitability.
Constraints on parasite fecundity and transmission in an insect‐STD system
Authors: J. Ryder Jonathan , Hathway Jenna , J. Knell Robert
Published: December 2007

Parasites that are sexually transmitted (causing sexually transmitted diseases, or STDs) can have important effects on host population dynamics, but we know almost nothing for such parasites about constraints on fecundity and transmission. In this study, we have examined the effect of two potentially important constraints in one of the few empirically well‐studied animal‐STD systems, the ladybird,Adalia bipunctata, and its sexually transmitted mite,Coccipolipus hippodamiae. Using a factorial design, we manipulated: (i) within‐host competition, by varying infection intensity; and (ii) host condition, by introducing dietary stress. Infection withC.hippodamiaesignificantly reduced ladybird survival whether or not diet was restricted, and restricting diet led to reduced survival regardless of infection status. Increased infection intensity and reduced host condition (dietary stress) both independently constrained per capita rates of parasite egg production and the development of infective larvae. Furthermore, when host condition was compromised, significantly fewer larvae were transmitted per adult mite during copulation. The effect of infection intensity on per mite transmission was more complex: there was no significant effect when hosts were fed normally, but when the ladybirds were nutritionally stressed higher infection intensity was associated with a slight increase in the numbers that were transmitted (despite the fact that mite fecundity was reduced under these conditions). These results indicate that host condition and within‐host competition may both play an important role in shaping the epidemiology of theA.bipunctata–C.hippodamiaesystem, by influencing the parasite's basic reproductive ratio (R0) and the rate of epidemic spread. Our data also extend general insights into STD ecology, by highlighting the importance of constraints on disease dynamics that are likely to be widespread.
Latitudinal variation in plant–herbivore interactions in European salt marshes
Authors: Pennings Steven C. , Zimmer Martin , Dias Natália , Sprung Martin , Davé Nilam , Ho Chuan‐Kai , Kunza Amy , McFarlin Caroline , Mews Malte , Pfauder Anett , Salgado Cristiano
Published: December 2007

Ecological interactions often vary geographically. Work in salt marshes on the Atlantic Coast of the United States has documented community‐wide latitudinal gradients in plant palatability and plant traits that may be driven in part by greater herbivore pressure at low latitudes. To determine if similar patterns exist elsewhere, we studied six taxa of saltmarsh plants (Atriplex, Juncus, Limonium, Salicornia, Spartina and Suaeda) at European sites at high (Germany and the Netherlands) and low (Portugal and Spain) latitudes. We conducted feeding assays using both native and non‐native consumers, and documented patterns of herbivore damage in the field. As in the United States, high‐latitude plants tended to be more palatable than low‐latitude plants when offered to consumers in paired feeding assays in the laboratory, although assays with grasshopper consumers were less consistent than those with crab consumers, and plants in the field at low‐latitude sites tended to experience greater levels of herbivore pressure than plants at high‐latitude sites. Similarly, high‐latitude leaf litter was more palatable than litter from low‐latitude plants when offered to consumers in paired feeding assays in the laboratory. Latitudinal gradients in plant palatability and herbivore pressure may be a general phenomenon, and may contribute to latitudinal gradients in decomposition processes.
A mathematical and statistical framework for modelling dispersal
Authors: Snäll Tord , B. O'Hara Robert , Arjas Elja
Published: December 2007

Mechanistic and phenomenological dispersal modelling of organisms has long been an area of intensive research. Recently, there has been an increased interest in intermediate models between the two. Intermediate models include major mechanisms that affect dispersal, in addition to the dispersal curve of a phenomenological model. Here we review and describe the mathematical and statistical framework for phenomenological dispersal modelling. In the mathematical development we describe modelling of dispersal in two dimensions from a point source, and in one dimension from a line or area source. In the statistical development we describe applicable observation distributions, and the procedures of model fitting, comparison, checking, and prediction. The procedures are also demonstrated using data from dispersal experiments. The data are hierarchically structured, and hence, we fit hierarchical models. The Bayesian modelling approach is applied, which allows us to show the uncertainty in the parameter estimates and in predictions. Finally, we show how to account for the effect of wind speed on the estimates of the dispersal parameters. This serves as an example of how to strengthen the coupling in the modelling between the phenomenon observed in an experiment and the underlying process – something that should be striven for in the statistical modelling of dispersal.
Collapse of an ant–scale mutualism in a rainforest on Christmas Island
Authors: Abbott Kirsti L. , Green Peter T.
Published: December 2007

Positive interactions play a widespread role in facilitating biological invasions. Here we use a landscape–scale ant exclusion experiment to show that widespread invasion of tropical rainforest by honeydew‐producing scale insects on Christmas Island (Indian Ocean) has been facilitated by positive interactions with the invasive ant Anoplolepisgracilipes. Toxic bait was used to exclude A. gracilipes from large (9–35 ha) forest patches. Within 11 weeks, ant activity on the ground and on trunks had been reduced by 98–100%, while activity on control plots remained unchanged. The exclusion of ants caused a 100% decline in the density of scale insects in the canopies of three rainforest trees in 12 months (Inocarpus fagifer, Syzygiumnervosum and Barringtonia racemosa), but on B. racemosa densities of scale insects also declined in control plots, resulting in no effect of ant exclusion on this species. This study demonstrates the role of positive interactions in facilitating biological invasions, and supports recent models calling for greater recognition of the role of positive interactions in structuring ecological communities.
Soil water partitioning contributes to species coexistence in tallgrass prairie
Authors: Nippert Jesse B. , Knapp Alan K.
Published: December 2007

The majority of tallgrass prairie root biomass is located in the upper soil layers (0–25 cm), but species differences exist in reliance on soil water at varying depths. These differences have led to the hypothesis that resource partitioning belowground facilitates species co‐existence in this mesic grassland. To determine if plant water relations can be linked to soil water partitioning as a potential mechanism allowing C3species to persist among the more dominant C4grasses, we measured differences in the source of water‐use using the isotopic signature of xylem water, volumetric soil water content at 4 depths, and leaf water potentials. Data were collected for seven species representing C4grasses, C3forbs and C3shrubs over three growing seasons at the Konza Prairie (Kansas, USA) to encompass a range of natural climatic conditions. C4grasses relied on shallow soil water (5 cm) across the growing season and had midday leaf water potentials that were highly correlated with shallow soil water regardless of soil water availability at other portions of the soil profile (20, 40 and 90 cm). In contrast, C3species only used shallow soil water when plentiful at this depth; these species increased their dependence on soil water from greater depths as the upper soil layers dried. Structural equation models describing plant water relations were very similar for the three C4species, whereas a unique set of models and drivers were identified for each of the C3species. These results support soil water partitioning as a mechanism for species coexistence, as C4species in this grassland have relatively consistent dependence on water in shallow soil layers, whereas C3species show niche differentiation in water use strategies to avoid competition with C4grasses for water in shallow soil layers when this resource is limiting and leaf water stress is high.
Generalist diurnal pollination provides greater fitness in a plant with nocturnal pollination syndrome: assessing the effects of a Silene – Hadena interaction
Authors: Giménez‐Benavides Luis , Dötterl Stefan , Jürgens Andreas , Escudero Adrián , Iriondo José M.
Published: December 2007

Nursery pollination in Caryophyllaceae species by Hadena and Perizoma moths has been extensively described in the last few decades. Evidence across multiple pairs of species shows that such pollination systems constitute relatively specialized interactions, shifting between parasitism and mutualism depending on the presence of effective co‐pollinators.

In this work, we describe a new specific Silene–Hadena interaction, the Silene ciliata–Hadena consparcatoides system. Although S. ciliata presents a typical nocturnal pollination syndrome, diurnal flower visitors have also been recorded, which motivated us to evaluate the costs and benefits of this nursery moth pollination to the plant. We experimentally induced two pollination regimes at non‐overlapping day‐night periods in a natural population of S. ciliata, and compared their effects on plant reproductive success from flower to seedling stages. Flower scent composition of S. ciliata and antennal responses of H. consparcatoides to this scent were recorded to evaluate the specificity of olfactory signals in this interaction system.

In accordance with its nocturnal pollination syndrome, S. ciliata emitted a greater amount of flower scent compounds during the night. Some of the predominant scent compounds, such as benzaldehyde, benzyl acetate and methyl salicylate elicited signals in the antennae of H. consparcatoides. Diurnal pollination produced more fruits per flower than nocturnal pollination, but the latter produced higher brood size resulting in similar overall fecundity. However, seeds generated from diurnal pollination were heavier and germinated better. We conclude that despite its nocturnal pollination syndrome, S. ciliata achieved similar reproductive success and higher offspring vigour under the diurnal pollinator regime. Although H. consparcatoides is specialized in S. ciliata, its shortage or absence would not jeopardize the reproductive success of its host plant. On the contrary, the seed predation exerted by this nursery pollinator shifts the interaction towards parasitism.
Benefits associated with the domatia mediated tritrophic mutualism in the shrub Coprosma lucida
Authors: Monks Adrian , O'Connell Dean M. , Lee William G. , Bannister Jennifer M. , Dickinson Katharine J. M.
Published: December 2007

The fitness benefits of plant structural adaptations that increase the effectiveness of fungivores against leaf pathogenic fungi are poorly understood. In a 12‐month field experiment, we investigated the effect of domatia on mite density, the role of these mites in limiting leaf fungi, and the associated effects on plant fitness in the endemic New Zealand shrub, Coprosma lucida. The presence of domatia on mite density was controlled using combinations of domatia blocking, sham blocking, mite addition and mite control using miticide. Limiting access to domatia reduced mite density and increased the proportion of leaves without mites. Mite families represented were predominantly fungivorous/detritivorous (97.2%), and predaceous (2.6%); herbivorous mites were absent. Mites significantly reduced fungal hyphae, fungal spores and pollen, but the effect was surface‐(upper/lower) and density‐dependent with the greatest reduction in fungi occurring over low mite densities. Fungal hyphae reduced leaf longevity, but were associated with increased production of new leaves. Hyphae density on old leaves was negatively correlated with the number of domatia produced on new leaves. New leaves in the mite reduction treatment had slightly reduced levels of carbon but not nitrogen. High levels of fungal infection on the lower surface increased the number of fruit fascicles per shoot, however on the upper surface where fungi were reduced by mites, hyphae density was negatively related to reproduction. The data support a limited interpretation of a fitness benefit for plants with domatia. While domatia increased mite density, control of fungi by mites occurred at lower average densities than supported by plants without functioning domatia. We suggest the primary function of leaf domatia in this mutualism is to increase the probability of a leaf‐level beneficial mite presence rather than to maximise mite density. Many mites are not necessarily better than few mites, but some mites are better than none.
Dominance by a canopy forming seaweed modifies resource and consumer control of bloom‐forming macroalgae
Authors: Klemens Eriksson Britas , Rubach Anja , Hillebrand Helmut
Published: December 2007

Degradation of ecological resources by large‐scale disturbances highlights the need to demonstrate biological properties that increase resistance to change and promote the resilience of ecosystem regimes. Coastal eutrophication is a global‐scale disturbance that drives ecosystem change by increasing primary production and favouring ephemeral and bloom‐forming life‐forms. Recent synthesis indicates that consumption processes increase the resistance of coastal communities to nutrient loading by controlling the responses of ephemeral macroalgae. Here we suggest a similar ecological function for canopy cover by demonstrating that the presence of a canopy species modifies both resource and consumer control of bloom‐forming algae associated with nutrient enrichment. We tested effects of canopy presence on the interaction between consumer and resource control, by field‐manipulations of a dominant canopy forming seaweed (Fucus vesiculosus), grazer presence (dominated by the gastropodLittorina littorea) and nutrient enrichment (common agricultural NPK fertilizer). Canopy cover and grazers jointly controlled strong increases of ephemeral bloom‐forming algae (dominated byUlvaspp) from nutrient enrichment; nutrients increased ephemeral recruitment almost 10‐fold, but only in the absence of both grazers and canopy cover. Recruitment success of the canopy‐forming seaweed itself decreased additively with 56.1, 71.3 and 50.5% from independent effects of canopy cover, grazers and nutrient enrichment, respectively. A meta‐analysis of nine nutrient enrichment experiments including seaweed, seagrass and stream communities, showed that in the presence of canopies average nutrient effects were reduced by more than 90% compared to without canopies. This corroborates the generality of our finding that dominating canopy species are important for aquatic ecosystems by increasing community resistance to the propagation of nutrient effects.
The consequences of the variance‐mean rescaling effect on effective population size
Authors: Pertoldi C. , A. Bach L. , S. F. Barker J. , Lundberg P. , Loeschcke V.
Published: December 2007

The effective population size (Ne), and the ratio between Ne and census population size (N) are often used as measures of population viability. We show that using the harmonic mean of population sizes over time – a common proxy for Ne– has some important evolutionary consequences and implications for conservation management. This stems from the fact that there is no unambiguous relationship between the arithmetic and harmonic means for populations fluctuating in size. As long as the variance of population size increases moderately with increasing arithmetic mean population size, the harmonic mean also increases. However, if the variance of population size increases more rapidly, which existing data often suggest, then the harmonic mean may actually decrease with increasing arithmetic mean. Thus maximizing N may not maximize Ne, but could instead lower the adaptive potential and hence limit the evolutionary response to environmental change. Large census size has the clear advantage of lowering demographic stochasticity, and hence extinction risk, and under certain conditions large census size also minimizes the loss of genetic variation. Consequently, maximising census size has served as a useful dogma in ecology, genetics and conservation. Nonetheless, due to the intricate relationships among Ne, population viability and the properties of population fluctuations, we suggest that this dogma should be taken only as a rule of thumb.
How to write consistently boring scientific literature
Authors: Sand‐Jensen Kaj
Published: December 2007

Although scientists typically insist that their research is very exciting and adventurous when they talk to laymen and prospective students, the allure of this enthusiasm is too often lost in the predictable, stilted structure and language of their scientific publications. I present here, a top‐10 list of recommendations for how to write consistently boring scientific publications. I then discuss why we should and how we could make these contributions more accessible and exciting.
The complementarity of single‐species and ecosystem‐oriented research in conservation research
Authors: B. Lindenmayer David , Fischer Joern , Felton Adam , Montague‐Drake Rebecca , D. Manning Adrian , Simberloff Dan , Youngentob Kara , Saunders Debbie , Wilson David , M. Felton Annika , Blackmore Caroline , Lowe Arianne , Bond Suzi , Munro Nicki , P. Elliott Carole
Published: December 2007

There has been much debate about the relative merits of single‐species vs ecosystem‐oriented research for conservation. This debate has become increasingly important in recent times as resource managers and policy makers in some jurisdictions focus on ecosystem‐level problems. We highlight the potential strengths and limitations of both kinds of research, discuss their complementarity and highlight problems that may arise where competition occurs between the two kinds of research.

While a combination of approaches is ideal, a scarcity of funding, time, and expertise means it is impossible to study and manage each species, ecological process, or ecological pattern separately. Making decisions about priorities for the kinds of research, priorities for the kinds of conservation management, and associated allocation of scarce funds is a non‐trivial task. We argue for an approach whereby limited resources for conservation research are targeted at projects most likely to close important knowledge gaps, while also promoting ongoing synergies between single‐species and ecosystem‐oriented research.
Publication bias and merit in ecology
Authors: Lortie C. J. , Aarssen L. W. , Budden A. E. , Koricheva J. K. , Leimu R. , Tregenza T.
Published: December 2007

Bias, or any set of factors that influence the general expression of merit, is common in science and is an inevitable by‐product of an imperfect but otherwise reasonably objective human pursuit to understand the world we inhabit. In this paper, we explore the conceptual significance of a relatively tractable form of bias, namely publication and dissemination bias. A specific definition is developed, a working model of classification for publication bias is proposed, and an assessment of what we can measure is described. Finally, we offer expectations for ecologists with respect to the significance of bias in the publication process within our discipline. We argue that without explicit consideration of both the qualitative and quantitative aspects of publication bias in ecology, we limit our capacity to fairly assess and best use the science that we as a community produce.
Disturbance and reef topography maintain high local diversity in Ecklonia radiata kelp forests
Authors: Toohey Benjamin D. , Kendrick Gary A. , Harvey Euan S.
Published: December 2007

Disturbance of competitive‐dominant plant and algae canopies often lead to increased diversity of the assemblage. Kelp forests, particularly those of temperate Western Australia, are habitats with high alpha diversity. This study investigated the roles of broad‐scale canopy loss and local scale reef topography on structuring the kelp‐dominated macroalgal forests in Western Australia. Eighteen 314 m2 circular areas were cleared of their Ecklonia radiata canopy and eighteen controls were established across three locations. The patterns of macroalgal recolonisation in replicate clearances were observed over a 34 month period. Macroalgal species richness initially increased after canopy removal with a turf of filamentous and foliose macroalgae dominating cleared areas for up to seven months. A dense Sargassum canopy dominated cleared areas from 11 to 22 months. By 34 months, partial recovery of the kelp canopy into cleared areas had occurred. Some cleared areas did not follow this trajectory but remained dominated by turfing, foliose and filamentous algae. As kelp canopies developed, the initial high species diversity declined but still remained elevated relative to undisturbed controls, even after 34 months. More complex reef topography was associated with greater variability in the algal assemblage between replicate quadrats suggesting colonising algae had a greater choice of microhabitats available to them on topographically complex reefs. Shading by canopies of either Sargassum spp. and E. radiata are proposed to highly influence the abundance of algae through competitive exclusion that is relaxed by disturbance of the canopy. Disturbance of the canopy in E. radiata kelp forests created a mosaic of different patch types (turf, Sargassum‐dominated, kelp‐dominated). These patch types were both transient and stable over the 34 months of this study, and are a potential contemporary process that maintains high species diversity in temperate kelp‐dominated reefs.
Pollen limitation affects progeny vigour and subsequent recruitment in the insect‐pollinated herb Ranunculus acris
Authors: Joar Hegland Stein , Totland Ørjan
Published: December 2007

Pollen limitation on seed production appears to be widespread among the angiosperms. However, few studies have examined if pollen limitation affects population growth. We supplementally hand‐pollinated all flowers of 20 individuals of Ranunculus acris in the temperate meadow Rudsviki, Kaupanger, west Norway in 2003. The seed production did not respond to pollen addition, but the achene weight increased by 18% after supplemental pollination. To test whether this progeny quality response to the pollen‐supplementation experiment could contribute to population growth, we sowed achenes from hand‐pollinated plants and control plants into natural conditions in ten blocks at three densities. During the subsequent season (2004), the number of seedlings and juveniles (pooled) from hand‐pollinated plants were substantially (64%) higher than from controls. There was also a clear positive effect of seed sowing‐density on recruitment, suggesting that recruitment is seed‐limited in this system. However, the density of vegetative individuals in 2005 was generally low and did not differ significantly between plots that received achenes from control or supplementary pollinated plants. Our results show that pollen limitation may affect germination through seed quality, and thereby impact plant population dynamics. However, in our system it appears that other factors, such as intra‐ and interspecific competition, may have outweighed the potential contribution from pollen limitation on population demography.
Rodents change acorn dispersal behaviour in response to ungulate presence
Authors: Muñoz Alberto , Bonal Raúl
Published: December 2007

Small rodents are prominent seed predators, but they also favour plant recruitment as seed dispersers. The direct interactions of ungulates on plants are more one‐sided and negative, as they mainly reduce plant recruitment through predation on seeds and seedlings. The effects of small rodents and ungulates on plant recruitment have been considered and studied as independent episodes within plant regeneration cycles. However, ungulate–rodent interactions and their potential effects on plant regeneration have not been considered so far. A number of studies have recently documented ungulate effects on the abundance, diversity and spatial distribution of small rodents. Here, we hypothesize that ungulates may also affect rodent seed dispersal behaviour. We monitored acorn dispersal by small rodents (Mus spretus and Apodemus sylvaticus) in oak woodlands with and without exclosures for large ungulates, mainly red deer, Cervus elaphus, and wild boar, Sus scrofa. The study was carried out in a typical Mediterranean Holm oak, Quercus ilex, forest throughout the acorn fall season in 2003 and 2004. We found that, in both years, the proportion of acorns cached and not recovered in the short‐term was, on average, lower in the presence (1.4%) than in the absence (19.9%) of ungulates. Acorn dispersal distances were not affected by ungulate presence in either year. However, ungulates had an effect on the spatial distribution of dispersed seeds; rodents apparently avoided shrubs as caching sites in both years. This result was interpreted as a behavioural response to reduce the risk of cache pilferage by conspecifics, which are closely associated with shrubs in presence, but not in absence, of ungulates. Potential effects of different densities of rodents or predators were discarded, as none of them differed between the areas with and without ungulates. The present study found significant interactions between heterospecific seed and seedling consumers that had been considered as independent episodes within tree regeneration cycles. As a result of such interactions, ungulates may have negative indirect effects on oak recruitment by reducing (1) acorn caching frequency, and (2) the proportion of acorns cached under shrubs, key nurse‐plants for the establishment of Holm oak seedlings in Mediterranean areas.
Life history tradeoffs in relation to the degree of polyandry and developmental pathway in Pieris napi (Lepidoptera, Pieridae)
Authors: Välimäki Panu , Kaitala Arja
Published: December 2007

Pieris napi females have different heritable reproductive tactics. Polyandrous females have higher lifetime fecundity, whereas monandrous ones start to reproduce at a faster rate. Butterfly larvae are time‐constrained in seasonal environments. Thus, polyandry is expected to be associated with fast juvenile development, which may result in biased mortality due to physiological costs. We compared how females with varying degrees of polyandry allocate between duration of larval period and achievable size in directly developing and over‐wintering generations. Offspring survival and growth were monitored under a high density and low quality diet. Polyandrous females developed at a faster rate than monandrous ones, regardless of developmental pathway. The growth rate of female offspring correlated with their mothers’ degree of polyandry, which underpins polyandry and monandry as distinct strategies with life history differences reaching beyond mating frequency. The high growth rate of polyandrous females resulted in a short larval period among directly developing females, and in large size within an over‐wintering cohort. A change in either the duration of the larval period or pupal mass had no significant effect on the other, emphasising that growth rate is not necessarily a simple outcome of the tradeoff between development time and size at maturity. The correlation between the degree of polyandry and juvenile growth rate diminished when larvae were exposed to environmental stress, which offers an explanation why juvenile mortality was decoupled from mating tactic. We conclude that polyandry is a strategy that allows larvae to utilise optimal conditions in a more effective way than monandry. As a consequence, polyandrous females either achieve larger size or they mature faster. This gives them a double advantage over monandrous ones within an over‐wintering generation or diminishes the effects of asynchronous hatching of offspring within a directly developing generation. Possible costs of high growth rate are discussed.
Perturbed partners: opposite responses of plant and animal mutualist guilds to inundation disturbances
Authors: Prinzing Andreas , Dauber Jens , Hammer Edith C. , Hammouti Nasera , Böhning‐Gaese Katrin
Published: December 2007

Mutualists have been suggested to play an important role in the assembly of many plant and animal communities, but it is not clear how this depends on environmental factors. Do, for instance, natural disturbances increase or decrease the role of mutualism? We focused on entire guilds of mutualists, studying seed‐dispersing ants and ant‐dispersed plants along gradients of inundation disturbances. We first studied how abundance and richness of the mutualists, relative to non‐mutualists, change along 35 small‐scale gradients of inundation disturbances. We found that at disturbed sites, mutualistic plant species, those that reproduce by seeds dispersed by ants, increased in abundance and in consequences in richness, relative to other herbaceous plants. In contrast, we found that among the epigeic arthropods the abundance of mutualists declined, even more so than other arthropods. Correspondingly, distributions of plant and animal mutualists became increasingly discordant at disturbed sites: most plant mutualists were spatially separated from most animal mutualists. We finally found that high abundances of plant mutualists did not translate into a high nutrition service rendered to ants: at disturbed sites, many of the plants of ant‐dispersed species did not produce seeds, which coincided with a decline in seed dispersal by ants and a changing searching behavior of the ants. Overall, the small‐scale natural disturbances we studied were correlated to a major change in the assembly of mutualist guilds. However, the correlation was often opposite between interacting plant and animal mutualist guilds and may thus reduce the potential interaction between them.
Temporal and spatial variability in soil food web structure
Authors: Berg Matty P. , Bengtsson Janne
Published: December 2007

Heterogeneity is a prominent feature of most ecosystems. As a result of environmental heterogeneity the distribution of many soil organisms shows a temporal as well as horizontal and vertical spatial patterning. In spite of this, food webs are usually portrayed as static networks with highly aggregated trophic groups over broader scales of time and space. The variability in food web structure and its consequences have seldom been examined. Using data from a Scots pine forest soil in the Netherlands, we explored (1) the temporal and spatial variability of a detrital food web and its components, (2) the effect of taxonomic resolution on the perception of variability over time and across space, and (3) the importance of organic matter quality as an explanatory factor for variability in food web composition. Compositional variability, expressed using the Bray‐Curtis similarity index, was measured over 2.5 years using a stratified litterbag design with three organic horizons per litterbag set.

Variability in community composition and organic matter degradation increased over time in the litter horizon only. Seasonal variation in community composition was larger than variation between samples from the same season in different years. Horizontal spatial variability in community composition and organic matter degradation was relatively low, with no increase in variability with increasing distance between samples. Vertically, communities and organic matter degradation was more different between the non‐adjacent litter and humus horizons than between adjacent layers.

These findings imply that soil food webs, at least in temperate forest plantations, are more variable than is currently appreciated in experiments and model studies, and that organic matter turnover might be an important factor explaining variability in community composition. Species composition was more variable than functional group composition, which implies that aggregated food webs will seem less sensitive to local temporal and spatial changes than they in fact are.
Population dynamic consequences of parasitised‐larval competition in stage‐structured host–parasitoid systems
Authors: White Steven M. , Sait Steven M. , Rohani Pejman
Published: December 2007

Parasitism can influence many aspects of the host's behaviour and physiology, which in turn can have a profound impact on their population and evolutionary ecology. In many host–parasite interactions there is often a time lag between infection and the death of the host, yet little is known, experimentally or theoretically, about the effects that intra‐class competition between parasitised and unparasitised hosts have on the host–parasite population dynamics.

In this article we address this gap in our understanding using a stage‐structured mathematical model for a host–parasitoid interaction, which has been parameterised for thePlodia–Venturiaexperimental system.

In the case where parasitised larvae do not compete and do not cannibalise unparasitised larvae, our model predicts a wide range of host–parasitoid dynamics, ranging from host–parasitoid generation cycles, to host generation cycles with parasitoid half‐generation cycles, to host–parasitoid equilibria, to host generation cycles with parasitoid extinction.

However, when parasitised larvae can compete with their unparasitised larvae counterparts, the host–parasitoid population dynamics can dramatically change. In particular, we show that high levels of competition exerted by unparasitised larvae upon parasitised larvae is more likely to lead to parasitoid extinction.

In addition, we demonstrate that unparasitised host larvae that are sufficiently susceptible to intra‐class competition, or parasitised host larvae that are sufficiently strong competitors, can have a stabilising effect on the host–parasitoid population dynamics.

The implications of these theoretical results are discussed in light of our understanding of host–parasitoid interactions and host–parasite systems in general.