Testing hypotheses in evolutionary ecology with imperfect detection: capture-recapture structural equation modeling

Studying evolutionary mechanisms in natural populations often requires testing multifactorial scenarios of causality involving direct and indirect relationships among individual and environmental variables. It is also essential to account for the imperfect detection of individuals to provide unbiased demographic parameter estimates. To cope with these issues, we developed a new approach combining structural equation models with capture-recapture models (CR-SEM) that allows the investigation of competing hypotheses about individual and environmental variability observed in demographic parameters. We employ Markov chain Monte Carlo sampling in a Bayesian framework to (1) estimate model parameters, (2) implement a model selection procedure to evaluate competing hypotheses about causal mechanisms, and (3) assess the fit of models to data using posterior predictive checks. We illustrate the value of our approach using two case studies on wild bird populations. We first show that CR-SEM can be useful to quantify the action of selection on a set of phenotypic traits with an analysis of selection gradients on morphological traits in Common Blackbirds (Turdus merula). In a second case study on Blue Tits (Cyanistes caeruleus), we illustrate the use of CR-SEM to study evolutionary trade-offs in the wild, while accounting for varying environmental conditions.     

Occurrence and public perception of jellyfish along the German Baltic coastline

Jellyfish accumulations are often problematic for tourism and fisheries both along European coastlines and overseas. They damage the reputation of several seaside resorts and cause serious economic losses. On the German Baltic coast, jellyfish accumulations are well known, too. Besides population increase due to anthropogenic effects, normal hydrodynamic processes are notable key factors when it comes to jellyfish accumulations. Along German Baltic coastlines, moon jellyfish (Aurelia aurita) occur most frequently but also stinging lion??s mane jellyfish (Cyanea capillata) appear regularly, however not as abundant. The objectives of our study were a) to screen when, where, how many and which jellyfish species occur on German Baltic coasts, b) to find the causes for jellyfish accumulations and c) to evaluate how beach visitors perceive native medusae and whether information can influence their perception. Different methods where combined: systematic jellyfish observations in cooperation with lifeguards, investigations of jellyfish abundance in shallow water zones, and interviews with beach visitors. Our results suggest that jellyfish occurrence along the German Baltic coast correlates with offshore wind or shore-parallel wind, which cause upwelling events. In contrast, there is no evidence that frequency of jellyfish occurrence was dependent on water temperature in summer. In regard to tourism, we found that beach visitors who received information about jellyfish stated to feel significantly less bothered by medusae. Overall, this article addresses different methods to learn more about jellyfish accumulations and it shows information strategies in terms of improved beach management.     

Do evergreen and deciduous trees have different effects on net N mineralization in soil?

Evergreen and deciduous plants are widely expected to have different impacts on soil nitrogen (N) availability because of differences in leaf litter chemistry and ensuing effects on net N mineralization (N(min)). We evaluated this hypothesis by compiling published data on net N(min) rates beneath co-occurring stands of evergreen and deciduous trees. The compiled data included 35 sets of co-occurring stands in temperate and boreal forests. Evergreen and deciduous stands did not have consistently divergent effects on net N(min) rates; net N(min) beneath deciduous trees was higher when comparing natural stands (19 contrasts), but equivalent to evergreens in plantations (16 contrasts). We also compared net N(min) rates beneath pairs of co-occurring genera. Most pairs of genera did not differ consistently, i.e., tree species from one genus had higher net N(min) at some sites and lower net N(min) at other sites. Moreover, several common deciduous genera (Acer, Betula, Populus) and deciduous Quercus spp. did not typically have higher net N(min) rates than common evergreen genera (Pinus, Picea). There are several reasons why tree effects on net N(min) are poorly predicted by leaf habit and phylogeny. For example, the amount of N mineralized from decomposing leaves might be less than the amount of N mineralized from organic matter pools that are less affected by leaf litter traits, such as dead roots and soil organic matter. Also, effects of plant traits and plant groups on net N(min) probably depend on site-specific factors such as stand age and soil type.     

Parasite transmission in complex communities: predators and alternative hosts alter pathogenic infections in amphibians

While often studied in isolation, host-parasite interactions are typically embedded within complex communities. Other community members, including predators and alternative hosts, can therefore alter parasite transmission (e.g., the dilution effect), yet few studies have experimentally evaluated more than one such mechanism. Here, we used data from natural wetlands to design experiments investigating how alternative hosts and predators of parasites mediate trematode (Ribeiroia ondatrae) infection in a focal amphibian host (Pseudacris regilla). In short-term predation bioassays involving mollusks, zooplankton, fish, larval insects, or newts, four of seven tested species removed 62-93% of infectious stages. In transmission experiments, damselfly nymphs (predators) and newt larvae (alternative hosts) reduced infection in P. regilla tadpoles by -50%, whereas mosquitofish (potential predators and alternative hosts) did not significantly influence transmission. Additional bioassays indicated that predators consumed parasites even in the presence of alternative prey. In natural wetlands, newts had similar infection intensities as P. regilla, suggesting that they commonly function as alternative hosts despite their unpalatability to downstream hosts, whereas mosquitofish had substantially lower infection intensities and are unlikely to function as hosts. These results underscore the importance of studying host-parasite interactions in complex communities and of broadly linking research on predation, biodiversity loss, and infectious diseases.     

Mechanisms of habitat segregation between an invasive and an indigenous mussel: settlement,post-settlement mortality and recruitment

The mussel Mytilus galloprovincialis is highly invasive worldwide, but displays varying degrees of local and regional coexistence with indigenous mussels through spatial habitat segregation. We investigated the roles of settlement, post-settlement mortality, juvenile growth and recruitment in partial habitat segregation between the invasive M. galloprovincialis and the indigenous mussel Perna perna on the south coast of South Africa. We used two study locations, Plettenberg Bay and Tsitsikamma, 70 km apart, with two sites (separated by 300–400 m) per location, each divided into three vertical zones. There were no significant effects in Tsitsikamma, where daily settlement and monthly recruitment were significantly lower than in Plettenberg Bay. In Plettenberg Bay, settlement (primary and secondary) and recruitment of both species decreased upshore. Post-settlement mortality was measured over two consecutive 6-day periods during a spring tide and a neap tide. For both species mortality was low on the low-shore. High-shore mortality was consistently low for M. galloprovincialis, but increased dramatically for P. perna during spring tide. No data were obtained for growth of P. perna, but juvenile M. galloprovincialis grew more slowly farther upshore. P. perna recruited mainly in spring and summer, with a peak in summer far greater than for M. galloprovincialis. Recruitment of M. galloprovincialis was more protracted, continuing through autumn and winter. Thus local coexistence is due to a combination of pre- and post-recruitment factors differing in importance for each species. P. perna is excluded from the high-shore by recruitment failure (low settlement, high mortality). High survival and slow growth in juveniles may allow large densities of M. galloprovincialis to accumulate there, despite low settlement rates. With no differences between species in settlement or mortality on the low-shore, exclusion of M. galloprovincialis from that zone is likely to be by post-recruitment processes, possibly strengthened by periodic heavy recruitments of P. perna. At larger scales, larval retention and protracted recruitment contribute to the success of M. galloprovincialis at Plettenberg Bay, while recruitment limitation may explain why M. galloprovincialis is less successful at other sites.     

Relevant scales of variability of the benthic allochthonous microalga Chrysophaeum taylorii

Chrysophaeum taylorii (Pelagophyceae) is an allochthonous benthic microalga recently recorded in the Mediterranean Sea. During summer, the occurrence of C. taylorii is usually visible to the naked eye due to the large amount of mucilage this species produces. Information on the spatio-temporal variability of this species and on the predictability of massive mucilage events is still scarce and requires to define ad hoc managing strategies of major bloom events. The aim of this work was to identify the relevant scales of variation in the abundance of C. taylorii abundance and to estimate the relative recurrence of its blooms, testing the hypothesis that mucilage was dependent on the cell density. The first approach was the identification of the most appropriate sampling procedure to estimate benthic cell abundance of C. taylorii. The second one was the estimation of the magnitude of variation in C. taylorii cell abundance attributable to each of several spatial (areas, sites, zones and replicates) and temporal scales (fortnights and years) in the Marine Protected Area of Tavolara Punta Coda Cavallo (Western Mediterranean Sea). The results indicate fortnight and year as the most relevant scales of variability in the cell abundance of C. taylorii and highlight the unimportance of small spatial scales (zone and replicates) to the species variability. The collected data also evidence the absence of a direct relationship between the cell density of C. taylorii and the production of mucilage. In conclusion, these results indicate that patterns in the cell abundance of C. taylorii vary notably depending on the considered scale and that future investigations on processes affecting its performance will need to consider the relevant scales of variation evidenced.     

Those outsiders: How downstream externalities affect public good provision

Some policy problems pit one group?s interests against another?s. One group may determine provision of a project (such as a dam) that benefits group members but hurts others. We introduce a model of such projects. In-group members may contribute to a common fund that benefits them as a public good. Benefits from the project may vary within the group. Provision has negative downstream externalities: contributions hurt agents outside the in-group (“Outsiders”), rendering them anti-social. Many models of social preferences predict that such externalities should reduce provision, although conditional cooperation or a preference for in-group members may counteract this. We test this model with a lab experiment using Outsiders with whom the in-group members have more and less contact. With homogeneous in-group benefits, the presence of negative downstream externalities reduces contributions by half when they have closer contact with Outsiders but not at all when they have had no contact. We introduce a rotating high-return position that allows subjects to trade favors. In this setting, contributions of non-privileged members diminish slightly when faced with the negative externality given closer contact with Outsiders, and not at all with less contact. Reciprocal giving occurs whether or not Outsiders are present.     

Incorporating basic needs to reconcile poverty and ecosystem services

Conservation managers frequently face the challenge of protecting and sustaining biodiversity without producing detrimental outcomes for (often poor) human populations that depend on ecosystem services for their well-being. However, mutually beneficial solutions are often elusive and can mask trade-offs and negative outcomes for people. To deal with such trade-offs, ecological and social thresholds need to be identified to determine the acceptable solution space for conservation. Although human well-being as a concept has recently gained prominence, conservationists still lack tools to evaluate how their actions affect it in a given context. We applied the theory of human needs to conservation by building on an extensive historical application of need approaches in international development. In an innovative participatory method that included focus groups and household surveys, we evaluated how human needs are met based on locally relevant thresholds. We then established connections between human needs and ecosystem services through key-informant focus groups. We applied our method in coastal East Africa to identify households that would not be able to meet their basic needs and to uncover the role of ecosystem services in meeting these. This enabled us to identify how benefits derived from the environment were contributing to meeting basic needs and to consider potential repercussions that could arise through changes to ecosystem service provision. We suggest our approach can help conservationists and planners balance poverty alleviation and biodiversity protection and ensure conservation measures do not, at the very least, cause serious harm to individuals. We further argue it can be used as a basis for monitoring the impacts of conservation on multidimensional poverty.