Echinacea angustifolia and its specialist ant‐tended aphid: a multi‐year study of manipulated and naturally‐occurring aphid infestation

1. The impact of herbivores on plant fitness depends on multiple ecological mechanisms, including interactions between herbivore guilds. 2. This study assessed the effects of a specialist aphid (Aphis echinaceae) on performance and foliar herbivore damage of a long‐lived perennial plant (Echinacea angustifolia) native to the North American tallgrass prairie. A 2‐year field experiment manipulating aphid infestation on 100 plants was compared with concurrent and past observations of unmanipulated plants in the same outdoor experimental plot. Because ants co‐occur with aphids, the experiment tested the combined effects of aphids and ants. 3. Neither manipulated nor naturally‐occurring aphid infestations led to measurable declines in plant performance. Results for foliar herbivore damage differed between experimental and observational studies: the occurrence of foliar herbivore damage decreased with aphid infestation in the first year of the experiment and increased with aphid infestation over 5 years in unmanipulated plants. 4. While the experimental results concur with other experiments of ant–hemipteran–herbivore relationships, the observational results suggest that ant–aphid interactions do not naturally play a major role in determining patterns of foliar herbivory in this system. This result demonstrates the value of using field observations to interpret the relevance of experimental results.     

Spatial patterns of trees in natural forests of East-Central Europe

The analysis of spatial patterns is one of the ways to estimate the role of competition among trees in forest dynamics. Three hypotheses concerning distribution patterns in old-growth stands were tested: (1) fine-scale spatial patterns of trees are regular; (2) patterns do not differ significantly from a random distribution, and (3) spatial patterns at larger scales are clumped because of site heterogeneity. Old-growth forest stands in Poland and the Czech Republic were analysed with a modified Ripley K function, using distribution maps of tree stems. Fine-scale spatial patterns (with distances among trees not exceeding 15 m) were usually intermediate between random and regular. Trends towards a regular distribution occurred more often among dead than among live individuals. No significant relationships between tree species were found at smaller scales; however, at larger scales (distances from 15–25 m) negative associations between some species were found. This reflects site heterogeneity rather than any direct influence of one tree species upon another.     

Ecological emergence of thermal clines in body size

The unprecedented rate of global warming requires a better understanding of how ecosystems will respond. Organisms often have smaller body sizes under warmer climates (Bergmann's rule and the temperature‐size rule), and body size is a major determinant of life histories, demography, population size, nutrient turnover rate, and food‐web structure. Therefore, by altering body sizes in whole communities, current warming can potentially disrupt ecosystem function and services. However, the underlying drivers of warming‐induced body downsizing remain far from clear. Here, we show that thermal clines in body size are predicted from universal laws of ecology and metabolism, so that size‐dependent selection from competition (both intra and interspecific) and predation favors smaller individuals under warmer conditions. We validate this prediction using 4.1 × 10⁶ individual body size measurements from French river fish spanning 29 years and 52 species. Our results suggest that warming‐induced body downsizing is an emergent property of size‐structured food webs, and highlight the need to consider trophic interactions when predicting biosphere reorganizations under global warming.     

Are the assemblages of tree pollination modes being recovered by tropical forest restoration?

Questions

Do the assemblages of pollination modes in restored (tree plantings) and secondary (naturally regenerated) forests change in comparison to primary forests, and how do these assemblages relate to species turnover at regional scale?

Location

Southeast region of Brazil.

Methods

We classified tree species found in a total of 40 forest sites (18 primary, 11 restored, 11 secondary) according to pollination mode, based on the literature. We calculated and compared functional dissimilarity distances, amounts of species and accumulated abundance of pollination modes, and functional indices of richness and evenness between forest types.

Results

Functional dissimilarity distances were much smaller than species dissimilarity distances within forest types (mean <20%, >80%, respectively), indicating a small variation in pollination modes between sites. Functional indices of richness and evenness did not differ between forest types. However, significant changes were found in the species and abundance proportions of several pollination modes. Primary forests were characterized by the predominance of generalized insect‐pollinated species, followed by secondary proportions of bee, wind and moth pollination; other pollination modes were underrepresented. In restored forests, reductions were found in generalized insect, moth, wind, fly, pollen‐consuming insect and very‐small insect pollination, whereas the species pollinated by bees and bats more than doubled. Smaller changes were found among secondary forests, including reductions in moth, fly and fig‐wasp pollination, whereas there were incremental changes in bee, beetle, big animal and small insect pollination.

Conclusions

Our results indicate a rather stable assemblage of pollination modes and also high ecological redundancy among trees regardless of the species replacement at the regional scale. Major changes among restored forests are probably in response to larger disturbance effects and/or restoration practices conducted in these sites. In contrast, smaller changes among secondary forests could be in response to smaller disturbance effects and natural selection processes, and also seem to suggest that highly resilient degraded areas are more likely to recuperate their functional diversity through natural regeneration alone. In both cases, however, efforts to recover such patterns should be encouraged to avoid possible negative effects in plant–pollinator interactions.     

Population genomics reveals multiple drivers of population differentiation in a sex‐role‐reversed pipefish

A major goal of molecular ecology is to identify the causes of genetic and phenotypic differentiation among populations. Population genomics is suitably poised to tackle these key questions by diagnosing the evolutionary mechanisms driving divergence in nature. Here, we set out to investigate the evolutionary processes underlying population differentiation in the Gulf pipefish, Syngnathus scovelli. We sampled approximately 50 fish from each of 12 populations distributed from the Gulf coast of Texas to the Atlantic coast of Florida and performed restriction‐site‐associated DNA sequencing to identify SNPs throughout the genome. After imposing quality and stringency filters, we selected a panel of 6348 SNPs present in all 12 populations, 1753 of which were not physically linked. We identified a genome‐wide pattern of isolation by distance, in addition to a more substantial genetic break separating populations in the Gulf of Mexico from those in the Atlantic. We also used several divergence outlier approaches and tests for genotype–environment correlations to identify 400 SNPs putatively involved in local adaptation. Patterns of phenotypic differentiation and variation diverged from the overall genomic pattern, suggesting that selection, phenotypic plasticity or demographic factors may be shaping phenotypes in distinct populations. Overall, our results suggest that population divergence is driven by a variety of factors in S. scovelli, including neutral processes and selection on multiple traits.     

Factors influencing the spatial patterns of vertebrate roadkill in South Africa: The Greater Mapungubwe Transfrontier Conservation Area as a case study

Few studies have investigated the factors that influence roadkill occurrence in developing countries. In 2013, we monitored a 100‐km section of the road (comprising the R572 and R521 regional highways and the D2662) that pass through the Greater Mapungubwe Transfrontier Conservation Area in South Africa, to assess the possible factors influencing roadkill. Over a period of 120 days, and across the three ecological seasons, we recorded 981 roadkills (rate = 0.08 roadkill/km/day) from four vertebrate taxonomic groups. We generated predictive models of roadkill from one combined data set that considered eight variables identified from the literature as potential correlates of roadkill. The model that included the distance of the fence from the road, habitat type adjacent to the road, and the presence of a hill in the road (i.e., elevation) or a bank on the side of the road best explained roadkill occurrence. More roadkill was predicted to occur in both open and dense mopane and dense mixed bushveld habitats, on a hill, when there was a bank on the side of the road, and as the distance between the road verge and a fence decreased. Our model provides some insight into the significant predictors of roadkill occurrence and is therefore a valuable tool in identifying sites of high‐potential roadkill frequency and formulating mitigation measures for reducing road mortalities.     

Historical biogeography of the coffee family (Rubiaceae,Gentianales) in Madagascar: case studies from the tribes Knoxieae,Naucleeae, Paederieae and Vanguerieae

Aim In Madagascar the family Rubiaceae includes an estimated 650 species representing 95 genera. As many as 98% of the species and 30% of the genera are endemic. Several factors make the Rubiaceae a model system for developing an understanding of the origins of the Malagasy flora. Ancestral area distributions are explicitly reconstructed for four tribes (Knoxieae, Naucleeae, Paederieae and Vanguerieae) with the aim of understanding how many times, and from where, these groups have originated in Madagascar. Location Indian Ocean Basin, with a focus on Madagascar. Methods Bayesian phylogenetic analyses are conducted on the four tribes. The results are used for reconstructing ancestral areas using dispersal–vicariance analyses. Phylogenetic uncertainties in the reconstructions are accounted for by conducting all analyses on the posterior distribution from the analyses. Results Altogether, 11 arrivals in Madagascar (one in Paederieae, five in Knoxieae, three in Vanguerieae, and two in Naucleeae) are reconstructed. The most common pattern is a dispersal event (followed by vicariance) from Eastern Tropical Africa. The Naucleeae and Paederieae in Madagascar differ and originate from Asia. Numerous out‐of‐Madagascar dispersals, mainly in the dioecious Vanguerieae, are reconstructed. Main conclusions The four tribes arrived several times in Madagascar via dispersal events from Eastern Tropical Africa, Southern Africa and Tropical Asia. The presence of monophyletic groups that include a number of species only found in Madagascar indicates that much endemism in the tribes results from speciation events occurring well after their arrival in Madagascar. Madagascar is the source of origin for almost all Rubiaceae found on the neighbouring islands of the Comoros, Mascarenes and Seychelles.     

Engineered variants of InlB with an additional leucine‐rich repeat discriminate between physiologically relevant and packing contacts in crystal structures of the InlB:MET complex

The physiological relevance of contacts in crystal lattices often remains elusive. This was also the case for the complex between the invasion protein internalin B (InlB) from Listeria monocytogenes and its host cell receptor, the human receptor tyrosine kinase (RTK) MET. InlB is a MET agonist and induces bacterial host cell invasion. Activation of RTKs generally involves ligand‐induced dimerization of the receptor ectodomain. The two currently available crystal structures of the InlB:MET complex show the same arrangement of InlB and MET in a 1:1 complex, but different dimeric 2:2 assemblies. Only one of these 2:2 assemblies is predicted to be stable by a computational procedure. This assembly is mainly stabilized by a contact between the Cap domain of InlB from one and the Sema domain of MET from another 1:1 complex. Here, we probe the physiological relevance of this interaction. We generated variants of the leucine‐rich repeat (LRR) protein InlB by inserting an additional repeat between the first and the second LRR. This should allow formation of the 1:1 complex but disrupt the potential 2:2 complex involving the Cap‐Sema contact due to steric distortions. A crystal structure of one of the engineered proteins showed that it folded properly. Binding affinity to MET was comparable to that of wild‐type InlB. The InlB variant induced MET phosphorylation and cell scatter like wild‐type InlB. These results suggest that the Cap‐Sema interaction is not physiologically relevant and support the previously proposed assembly, in which a 2:2 InlB:MET complex is built around a ligand dimer.     

Prediction of biodiversity hotspots in the Anthropocene: The case of veteran oaks

Over the past centuries, humans have transformed large parts of the biosphere, and there is a growing need to understand and predict the distribution of biodiversity hotspots influenced by the presence of humans. Our basic hypothesis is that human influence in the Anthropocene is ubiquitous, and we predict that biodiversity hot spot modeling can be improved by addressing three challenges raised by the increasing ecological influence of humans: (i) anthropogenically modified responses to individual ecological factors, (ii) fundamentally different processes and predictors in landscape types shaped by different land use histories and (iii) a multitude and complexity of natural and anthropogenic processes that may require many predictors and even multiple models in different landscape types. We modeled the occurrence of veteran oaks in Norway, and found, in accordance with our basic hypothesis and predictions, that humans influence the distribution of veteran oaks throughout its range, but in different ways in forests and open landscapes. In forests, geographical and topographic variables related to the oak niche are still important, but the occurrence of veteran oaks is shifted toward steeper slopes, where logging is difficult. In open landscapes, land cover variables are more important, and veteran oaks are more common toward the north than expected from the fundamental oak niche. In both landscape types, multiple predictor variables representing ecological and human‐influenced processes were needed to build a good model, and several models performed almost equally well. Models accounting for the different anthropogenic influences on landscape structure and processes consistently performed better than models based exclusively on natural biogeographical and ecological predictors. Thus, our results for veteran oaks clearly illustrate the challenges to distribution modeling raised by the ubiquitous influence of humans, even in a moderately populated region, but also show that predictions can be improved by explicitly addressing these anthropogenic complexities.