New aspects of grassland recovery in old‐fields revealed by trait‐based analyses of perennial‐crop‐mediated succession

Classical old‐field succession studies focused on vegetation changes after the abandonment of annual croplands or on succession after the elimination of cultivated crops. Perennial‐crop‐mediated succession, where fields are initially covered by perennial crops, reveals alternative aspects of old‐field succession theories. We tested the validity of classical theories of old‐field succession for perennial‐crop‐mediated succession. We formulated the following hypotheses: (1) functional diversity increases with increasing field age; (2) resource acquisition versus conservation trade‐off shifts toward conservation at community level during the succession; (3) the importance of spatial and temporal seed dispersal decreases during the succession; and (4) competitiveness and stress‐tolerance increases and ruderality decreases at community level during the succession. We studied functional diversity, trait distributions and plant strategies in differently aged old‐fields using chronosequence method. We found increasing functional richness and functional divergence, but also unchanged or decreasing functional evenness. We detected a shift from resource acquisition to resource conservation strategy of communities during the succession. The role of spatial and temporal seed dispersal was found to be important not only at the initial but also at latter successional stages. We found an increasing stress‐tolerance and a decreasing ruderality during succession, while the competitiveness remained unchanged at the community level. Despite the markedly different starting conditions, we found that classical and perennial‐crop‐mediated old‐field successions have some similarities regarding the changes of functional diversity, resource acquisition versus conservation trade‐off, and seed dispersal strategies. However, we revealed also the subsequent differences. The competitive character of communities remained stable during the succession; hence, the initial stages of perennial‐crop‐mediated succession can be similar to the middle stages of classical old‐field succession. Moreover, the occupied functional niche space and differentiation were larger in the older stages, but resources were not effectively utilized within this space, suggesting that the stabilization of the vegetation requires more time.     

Suitability of Molluscs as Bioindicators for Meadow‐ and Flood‐Channels of the Elbe‐Floodplains

The goals of the subproject “molluscs” within the inter‐disciplinary research project “Indicator systems for the characterisation and prediction of ecological changes in floodplain systems” were: – develop further existing mollusc‐based indicator systems of site quality and to test their transferability, – characterise grassland sites within the recent floodplains of three study areas along the Elbe River, – analyse the relationships between indicator species‐/groups and abiotic parameters, – compile and use selected species traits in the analytical process. The results clearly show several characteristic species groups related to the hydrology of the sites (i.e. inundation and desiccation regime) and on to the degree of agricultural use. These dependencies can be interpreted by the simultaneous analysis of the species traits. “Models” are proposed, that are applicable to nature protection measures at the landscape scale. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A community‐level test of the leaf‐height‐seed ecology strategy scheme in relation to grazing conditions

Question: Is the assumption of trait independence implied in Westoby's (1998) leaf‐height‐seed (LHS) ecology strategy scheme upheld in a Mediterranean grazing system dominated by annuals? Is the LHS approach applicable at the community level? Location: Northern Israel. Methods: LHS traits (specific leaf area [SLA], plant height and seed mass), and additional leaf traits (leaf dry matter content [LDMC], leaf area, and leaf content of nitrogen [LNC], carbon [LCC], and phosphorus [LPC]), were analyzed at the species and community levels. Treatments included manipulations of grazing intensity (moderate and heavy) and protection from grazing. We focused on species comprising 80% of biomass over all treatments, assuming that these species drive trait relationships and ecosystem processes. Results: At the species level, SLA and seed mass were negatively correlated, and plant height was positively correlated to LCC. SLA, seed mass, and LPC increased with protection from grazing. At the community level, redundancy analysis revealed one principal gradient of variation: SLA, correlated to grazing, versus seed mass and plant height, associated with protection from grazing. We divided community functional parameters into two groups according to grazing response: (1) plant height, seed mass, LDMC, and LCC, associated with protection from grazing, and (2) SLA, associated with grazing. Conclusions: The assumption of independence between LHS traits was not upheld at the species level in this Mediterranean grazing system. At the community level, the LHS approach captured most of the variation associated with protection from grazing, reflecting changes in dominance within the plant community.     

Impact of inter‐ and intra‐specific competition among larvae on larval,adult, and life‐table traits of Aedes aegypti and Aedes albopictus females

1. Few studies have taken a comprehensive approach of measuring the impact of inter‐ and intra‐specific larval competition on adult mosquito traits. In this study, the impact of competition among Aedes aegypti (L.) and A. albopictus (Skuse) was quantified over the entire life of a cohort. 2. Competitive treatments affected hatch‐to‐adult survivorship and the development time to adulthood of females for both species but affected the median wing length of females only for A. albopictus. Competitive treatments had no significant effect on the median adult female longevity nor were there any effects on other individual traits related to blood feeding and reproductive success. 3. Analysis of life table traits revealed no effect of competitive treatment on the net reproductive rate (R₀) but there were significant effects on the cohort generation time (T_c) and the cohort rate of increase (r) for both species. 4. Inter‐ and intra‐specific competition among Aedes larvae may produce individual and population‐level effects that are manifest in adults; however, benign conditions may enable resulting adults to compensate for some impacts of competition, particularly those affecting blood‐feeding success, fecundity, and the net reproductive rate, R₀. The effect of competition, therefore, affects primarily larva‐to‐adult survivorship and the larval development time, which in turn impacts the cohort generation time, T_c, and ultimately the cohort rate of increase, r. 5. The lack of effects of the larval rearing environment on adult longevity suggests that effects on vectorial capacity owing to longevity may be limited if adults have easy access to sugar and bloodmeals.     

Taxon‐biased diet preference in the ‘generalist’ beetle‐hunting wasp Cerceris rubida provides insights on the evolution of prey specialization in apoid wasps

Opportunism and specialization appear to be widespread in apoid wasps, although the factors affecting the diet preference (and thus explaining the degree of specialization) are still largely unknown. Four hypotheses that stressed the importance of the size, sex, habitat, and taxonomic identity of prey of the beetle‐hunting digger wasp, Cerceris rubida, were formulated and tested. The wasp population hunted for phytophagous beetles belonging to abundant families around the wasp nesting site. In practice, the prey appeared to be hunted only in two cultivated fields, thus habitat accounted for a majority of the observed diet. The size of wasps was furthermore correlated with the size of their prey, and thus this also accounted for the frequencies of hunted prey and the strong individual specialization for both taxa and size. However, in the exploited habitat, some species were significantly over‐hunted than expected and some other significantly avoided by the wasps, causing an unexpected major role of prey taxon on the probability of being hunted, over the other explanatory variables (body size, body shape, sex, availability). This contrasts to that found in other wasp species, which appear to select prey basing essentially on their ecology and size or their relative abundance (opportunism). The results obtained in the present study show that even an apparent ‘generalist’ predator may turn out to be taxonomically specialized. Together with a re‐evaluation of previous studies, our results further suggest that the effect of size constraints and the developmental plan of prey (holometaboulous versus hemimetabolous) may have promoted either taxonomic opportunism or specialization in different lineages of apoid wasps. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 544–558.     

Sexual selection on female ornaments in the sex‐role‐reversed Gulf pipefish (Syngnathus scovelli)

Understanding how selection acts on traits individually and in combination is an important step in deciphering the mechanisms driving evolutionary change, but for most species, and especially those in which sexual selection acts more strongly on females than on males, we have no estimates of selection coefficients pertaining to the multivariate sexually selected phenotype. Here, we use a laboratory‐based mesocosm experiment to quantify pre‐ and post‐mating selection on female secondary sexual traits in the Gulf pipefish (Syngnathus scovelli), a sexually dimorphic, sex‐role‐reversed species in which ornamented females compete for access to choosy males. We calculate selection differentials and gradients on female traits, including ornament area, ornament number and body size for three episodes of selection related to female reproductive success (number of mates, number of eggs transferred and number of surviving embryos). Selection is strong on both ornament area and ornament size, and the majority of selection occurs during the premating episode of selection. Interestingly, selection on female body size, which has been detected in previous studies of Gulf pipefish, appears to be indirect, as evidenced by a multivariate analysis of selection gradients. Our results show that sexual selection favours either many bands or larger bands in female Gulf pipefish.     

Next‐generation QTL mapping: crowdsourcing SNPs,without pedigrees

For many molecular ecologists, the mantra and mission of the field of ecological genomics could be encapsulated by the phrase ‘to find the genes that matter’ (Mitchell‐Olds 2001 ; Rockman 2012 ). This phrase of course refers to the early hope and current increasing success in the search for genes whose variation underlies phenotypic variation and fitness in natural populations. In the years since the modern incarnation of the field of ecological genomics, many would agree that the low‐hanging fruit has, at least in principle, been plucked: we now have several elegant examples of genes whose variation influences key adaptive traits in natural populations, and these examples have revealed important insights into the architecture of adaptive variation (Hoekstra et al. 2006 ; Shapiro et al. 2009 ; Chan et al. 2010 ). But how well will these early examples, often involving single genes of large effect on discrete or near‐discrete phenotypes, represent the dynamics of adaptive change for the totality of phenotypes in nature? Will traits exhibiting continuous rather than discrete variation in natural populations have as simple a genetic basis as these early examples suggest (Prasad et al. 2012 ; Rockman 2012 )? Two papers in this issue (Robinson et al. 2013 ; Santure et al. 2013 ) not only suggest answers to these questions but also provide useful extensions of statistical approaches for ecological geneticists to study the genetics of continuous variation in nature. Together these papers, by the same research groups studying evolution in a natural population of Great Tits (Parus major), provide a glimpse of what we should expect as the field begins to dissect the genetic basis of what is arguably the most common type of variation in nature, and how genome‐wide surveys of variation can be applied to natural populations without pedigrees.     

Long‐term colonization ecology of forest‐dwelling species in a fragmented rural landscape – dispersal versus establishment

Species colonization in a new habitat patch is an efficiency indicator of biodiversity conservation. Colonization is a two‐step process of dispersal and establishment, characterized by the compatibility of plant traits with landscape structure and habitat conditions. Therefore, ecological trait profiling of specialist species is initially required to estimate the relative importance of colonization filters. Old planted parks best satisfy the criteria of a newly created and structurally matured habitat for forest‐dwelling plant species. We sampled species in 230 ancient deciduous forests (source habitat), 74 closed‐canopy manor parks (target habitats), 151 linear wooded habitats (landscape corridors), and 97 open habitats (isolating matrix) in Estonia. We defined two species groups of interest: forest (107 species) and corridor specialists (53 species). An extra group of open habitat specialists was extracted for trait scaling. Differing from expectations, forest specialists have high plasticity in reproduction mechanisms: smaller seeds, larger dispersules, complementary selfing ability, and diversity of dispersal vectors. Forest specialists are shorter, less nutrient‐demanding and mycorrhizal‐dependent, stress‐tolerant disturbance‐sensitive competitors, while corridor specialists are large‐seeded disturbance‐tolerant competitors. About 40% of species from local species pools have immigrated into parks. The historic forest area, establishment‐related traits, and stand quality enhance the colonization of forest specialists. The openness of landscape and mowing in the park facilitate corridor specialists. Species traits in parks vary between a forest and corridor specialist, except for earlier flowering and larger propagules. Forest species are not dispersal limited, but they continue to be limited by habitat properties even in the long term. Therefore, the shady parts of historic parks should be appreciated as important forest biodiversity‐enhancing landscape structures. The habitat quality of secondary stands can be improved by nurturing a heterogeneous shrub and tree layer, and modest herb layer management.     

Latitudinal variation in the competition‐colonisation trade‐off reveals rate‐mediated mechanisms of coexistence

Theories of species coexistence often describe a trade‐off between colonising and competitive abilities. In sessile marine invertebrates, this trade‐off can manifest as trends in species distributions relative to the size of isolated patches of substrate. Based on their abilities to find available substrate and competitively exclude neighbours, good colonisers tend to dominate smaller patches, whereas better competitors tend to monopolise larger patches. In theory, species with equivalent colonising and competitive abilities should display similar distributions across patch sizes. We used patch size to observe this manifestation of the competition‐colonisation trade‐off over 20° of latitude. The trade‐off was more readily observed at lower latitudes and was proportional to the ‘ecological age’ of communities (i.e. the degree of resource acquisition and likelihood of species interactions). Results suggest that ecological age may mediate the prominence of stochastic or deterministic coexistence mechanisms and will depend on the rate of ecological processes.     

Biological characteristics of a non‐photoperiodic‐diapause strain of the cabbage beetle Colaphellus bowringi (Coleoptera: Chrysomelidae)

Comparison of biological characteristics between diapausing and non‐diapausing strains of insects provides some insights into the mechanisms regulating diapause. In this study, biological characteristics, especially diapause characteristics and life‐history traits, of a non‐photoperiodic‐diapause (NPD) strain of the cabbage beetle Colaphellus bowringi were compared with those of a normal, high‐diapause (HD) strain that enters diapause in response to either long day length or low temperature. The NPD strain did not enter diapause at any photoperiod at 22°C or higher, but still had a capacity to enter diapause at low temperatures. Although diapause could be induced in both strains by exposure to 20°C, the proportion of individuals having shorter diapause duration was greater in the NPD strain compared to the HD strain. The NPD strain had significantly lower hatching and larval survival rates, longer developmental duration of immature stages, smaller body size and lower longevity and female fecundity compared to the HD strain. The NPD strain of this species is a promising model for investigating diapause regulation in insects in general.     

Trait‐based life strategies,ecological niches,and niche overlap in the nekton of the data‐poor Mediterranean Sea

Biological traits can determine species ecological niches and define species responses to environmental variation. Species have a specific functional position in the biological community, resulting in interactions like interspecific competition. In this study, we used biological traits in order to define the life strategies of 205 nektonic species of the Mediterranean Sea. Furthermore, traits related to resource use were analyzed to determine the level of trait and niche overlap and their relationship to life strategies. Focusing on habitats of importance (Posidonia beds, coralligène formations, and lagoons), we investigated strategies and niches of the species present there. Finally, we examined the life strategy of Lessepsian species and investigated the niche overlap between them and indigenous species. Archetypal analysis indicated the existence of three life histories corresponding to strategies already documented for fish (equilibrium, periodic, and opportunistic), with some species also placed in intermediate positions. Niche overlap was evaluated by multiple correspondence analysis and the generation of a single distance metric between all species pairs. This identified species occupying relatively empty (underexploited) ecological niches, like the Lessepsian species Siganus luridus and S. rivulatus, a finding that can also be associated with their establishment in the Mediterranean. Most Lessepsian species were associated with the opportunistic life history strategy, again an important aspect related to their establishment. Also, we documented that most species occurring in important habitats have a relatively high overlap of niches. No significant differences were found in the life strategies across Mediterranean habitats; however, variation in niche overlap and traits related to habitat use was detected. The findings can be useful to determine theoretical competition between species and to identify empty ecological niches. Fisheries science can also benefit from comprehending the dynamics of competing stocks or predict the responses of data‐poor stocks to anthropogenic stressors from known examples of species with shared life strategies.     

Trade‐offs between life‐history traits at range‐edge and central locations

The allocation of resources to different life‐history traits should represent the best compromise in fitness investment for organisms in their local environment. When resources are limiting, the investment in a specific trait must carry a cost that is expressed in trade‐offs with other traits. In this study, the relative investment in the fitness‐related traits, growth, reproduction and defence were compared at central and range‐edge locations, using the seaweed Ascophyllum nodosum as a model system. Individual growth rates were similar at both sites, whereas edge populations showed a higher relative investment in reproduction (demonstrated by a higher reproductive allocation and extended reproductive periods) when compared to central populations that invested more in defence. These results show the capability of A. nodosum to differentially allocate resources for different traits under different habitat conditions, suggesting that reproduction and defence have different fitness values under the specific living conditions experienced at edge and central locations. However, ongoing climate change may threaten edge populations by increasing the selective pressure on specific traits, forcing these populations to lower the investment in other traits that are also potentially important for population fitness.     

Variation in bulk‐leaf 13C discrimination,leaf traits and water‐use efficiency–trait relationships along a continental‐scale climate gradient in Australia

Large spatial and temporal gradients in rainfall and temperature occur across Australia. This heterogeneity drives ecological differentiation in vegetation structure and ecophysiology. We examined multiple leaf‐scale traits, including foliar ¹³C isotope discrimination (Δ¹³C), rates of photosynthesis and foliar N concentration and their relationships with multiple climate variables. Fifty‐five species across 27 families were examined across eight sites spanning contrasting biomes. Key questions addressed include: (i) Does Δ¹³C and intrinsic water‐use efficiency (WUE_i) vary with climate at a continental scale? (ii) What are the seasonal and spatial patterns in Δ¹³C/WUE_i across biomes and species? (iii) To what extent does Δ¹³C reflect variation in leaf structural, functional and nutrient traits across climate gradients? and (iv) Does the relative importance of assimilation and stomatal conductance in driving variation in Δ¹³C differ across seasons? We found that MAP, temperature seasonality, isothermality and annual temperature range exerted independent effects on foliar Δ¹³C/WUE_i. Temperature‐related variables exerted larger effects than rainfall‐related variables. The relative importance of photosynthesis and stomatal conductance (g_s) in determining Δ¹³C differed across seasons: Δ¹³C was more strongly regulated by g_s during the dry‐season and by photosynthetic capacity during the wet‐season. Δ¹³C was most strongly correlated, inversely, with leaf mass area ratio among all leaf attributes considered. Leaf N_mass was significantly and positively correlated with MAP during dry‐ and wet‐seasons and with moisture index (MI) during the wet‐season but was not correlated with Δ¹³C. Leaf P_mass showed significant positive relationship with MAP and Δ¹³C only during the dry‐season. For all leaf nutrient‐related traits, the relationships obtained for Δ¹³C with MAP or MI indicated that Δ¹³C at the species level reliably reflects the water status at the site level. Temperature and water availability, not foliar nutrient content, are the principal factors influencing Δ¹³C across Australia.     

Trait‐based approach confirms the importance of propagule limitation and assembly rules in old‐field restoration

Community assembly theory is suggested as a guiding principle for ecological restoration to help understand the mechanisms that structure biological communities and identify where restoration interventions are needed. We studied three hypotheses related to propagule limitation, stress‐dominance, and limiting similarity concepts in community assembly in a restoration field experiment with a trait‐based null model approach. The experiment aimed to assist the recovery of sand grassland on former arable land in the Kiskunság, Pannonian biogeographic region, Europe. Treatments included initial seeding of five grassland species, carbon amendment, low‐intensity mowing, and combinations in 1 m by 1 m plots in three old fields from 2003 to 2008. The distribution of 10 individual plant traits was compared to the null model and the effect of time and treatments were tested with linear mixed effect models. Initial seeding had the most visible impact on species and trait composition confirming propagule limitation in grassland recovery. Reducing nutrient availability through carbon amendment strengthened trait convergence for length of flowering as expected based on the stress‐dominance hypothesis. Mowing changed trait divergence to convergence for plant height with a strengthening impact with time, supporting our hypothesis of increasing dominance of limiting similarity with time. Our results support the idea that community assembly is simultaneously influenced by propagule limitation and multiple trait‐based processes that act through different traits. The limited impact of manipulating environmental filtering and limiting similarity compared to seeding, however, supports the view that only targeting the dispersal and environmental filters in parallel would improve restoration outcome.     

Relationship between pre‐ and post‐copulatory traits in Salvator rufescens (Squamata: Teiidae)

Understanding pre‐ and post‐copulatory mechanisms of sexual selection can provide insights into the evolution of male reproductive strategies. The phenotype‐linked fertility hypothesis postulates that male sperm quality and secondary sexual characteristics will positively co‐vary, whereas the sperm competition hypothesis predicts a negative association between those traits. Male reproductive traits often show variation throughout the reproductive period, suggesting that the relationship between pre‐ and post‐copulatory sexual selection may vary temporally. Here, we evaluated the relationship between secondary sexual character and sperm traits and its temporal variation in Salvator rufescens, a south American lizard. We observed a negative relationship between jaw muscle and principal piece length of sperm and a variation in the relationship between pre‐ and post‐copulatory traits throughout the reproductive period. Collectively, our results evidenced a trade‐off between pre‐ and post‐copulatory traits and a strong seasonal flexibility of male reproductive strategies in this lizard species.     

Trait‐mediated effects of predation across life‐history stages in container mosquitoes

1. It was determined if the predatory midge Corethrella appendiculata Grabham imposes a fitness cost in a native mosquito, Ochlerotatus triseriatus Say, and an invasive mosquito, Aedes albopictus Skuse. The hypothesis that decreased activity of immature prey in the presence of predator cues is associated with life history costs through all life cycle stages was tested. 2. In experiment 1, individual larvae of O. triseriatus or A. albopictus were raised in the presence or absence of predation cues at two resource levels. Prey were video recorded to detect behavioural responses and to measure development time, size at emergence, and adult longevity. In experiment 2, prey populations were reared in similar environments and the frequency of predator cue additions was varied. 3. Only O. triseriatus reduced its activity in the presence of predation cues. Predation cues were associated with longer immature development times and shorter adult life spans in O. triseriatus, whereas in A. albopictus, the cues were associated with a larger size of emerging adults. 4. In the present study, it was found that behavioural modifications during the larval stage can affect mosquitoes through multiple stages of their complex life cycle. The species‐specific behavioural differences are probably attributable to the longer evolutionary history O. triseriatus has with predators, relative to the invasive A. albopictus.     

Short‐range phenotypic divergence among genetically distinct parapatric populations of an Australian funnel‐web spider

Speciation involves divergence at genetic and phenotypic levels. Where substantial genetic differentiation exists among populations, examining variation in multiple phenotypic characters may elucidate the mechanisms by which divergence and speciation unfold. Previous work on the Australian funnel‐web spider Atrax sutherlandi Gray (2010; Records of the Australian Museum 62 , 285–392; Mygalomorphae: Hexathelidae: Atracinae) has revealed a marked genetic structure along a 110‐kilometer transect, with six genetically distinct, parapatric populations attributable to past glacial cycles. In the present study, we explore variation in three classes of phenotypic characters (metabolic rate, water loss, and morphological traits) within the context of this phylogeographic structuring. Variation in metabolic and water loss rates shows no detectable association with genetic structure; the little variation observed in these rates may be due to the spiders’ behavioral adaptations (i.e., burrowing), which buffer the effects of climatic gradients across the landscape. However, of 17 morphological traits measured, 10 show significant variation among genetic populations, in a disjunct manner that is clearly not latitudinal. Moreover, patterns of variation observed for morphological traits serving different organismic functions (e.g., prey capture, burrowing, and locomotion) are dissimilar. In contrast, a previous study of an ecologically similar sympatric spider with little genetic structure indicated a strong latitudinal response in 10 traits over the same range. The congruence of morphological variation with deep phylogeographic structure in Tallaganda's A. sutherlandi populations, as well as the inconsistent patterns of variation across separate functional traits, suggest that the spiders are likely in early stages of speciation, with parapatric populations independently responding to local selective forces.