Detection experiments with humans implicate visual predation as a driver of colour polymorphism dynamics in pygmy grasshoppers

Background: Animal colour patterns offer good model systems for studies of biodiversity and evolution of local adaptations. An increasingly popular approach to study the role of selection for camouflage for evolutionary trajectories of animal colour patterns is to present images of prey on paper or computer screens to human 'predators'. Yet, few attempts have been made to confirm that rates of detection by humans can predict patterns of selection and evolutionary modifications of prey colour patterns in nature. In this study, we first analyzed encounters between human 'predators' and images of natural black, grey and striped colour morphs of the polymorphic Tetrix subulata pygmy grasshoppers presented on background images of unburnt, intermediate or completely burnt natural habitats. Next, we compared detection rates with estimates of capture probabilities and survival of free-ranging grasshoppers, and with estimates of relative morph frequencies in natural populations.Results: The proportion of grasshoppers that were detected and time to detection depended on both the colour pattern of the prey and on the type of visual background. Grasshoppers were detected more often and faster on unburnt backgrounds than on 50% and 100% burnt backgrounds. Striped prey were detected less often than grey or black prey on unburnt backgrounds; grey prey were detected more often than black or striped prey on 50% burnt backgrounds; and black prey were detected less often than grey prey on 100% burnt backgrounds. Rates of detection mirrored previously reported rates of capture by humans of free-ranging grasshoppers, as well as morph specific survival in the wild. Rates of detection were also correlated with frequencies of striped, black and grey morphs in samples of T. subulata from natural populations that occupied the three habitat types used for the detection experiment.Conclusions: Our findings demonstrate that crypsis is background-dependent, and implicate visual predation as an important driver of evolutionary modifications of colour polymorphism in pygmy grasshoppers. Our study provides the clearest evidence to date that using humans as 'predators' in detection experiments may provide reliable information on the protective values of prey colour patterns and of natural selection and microevolution of camouflage in the wild

Decoration Increases the Conspicuousness of Raptor Nests

Avian nests are frequently concealed or camouflaged, but a number of species builds noticeable nests or use conspicuous materials for nest decoration. In most cases, nest decoration has a role in mate choice or provides thermoregulatory or antiparasitic benefits. In territorial species however, decorations may serve additional or complementary functions, such as extended phenotypic signaling of nest-site occupancy and social status to potential intruders. The latter may benefit both signaler and receiver by minimizing the risk of aggressive interactions, especially in organisms with dangerous weaponry. Support for this hypothesis was recently found in a population of black kites (Milvus migrans), a territorial raptor that decorates its nest with white artificial materials. However, the crucial assumption that nest decorations increased nest-site visibility to conspecifics was not assessed, a key aspect given that black kite nests may be well concealed within the canopy. Here, we used an unmanned aircraft system to take pictures of black kite nests, with and without an experimentally placed decoration, from different altitudes and distances simulating the perspective of a flying and approaching, prospecting intruder. The pictures were shown to human volunteers through a standardized routine to determine whether detection rates varied according the nest decoration status and distance. Decorated nests consistently showed a higher detection frequency and a lower detection-latency, compared to undecorated versions of the same nests. Our results confirm that nest decoration in this species may act as a signaling medium that enhances nest visibility for aerial receivers, even at large distances. This finding complements previous work on this communication system, which showed that nest decoration was a threat informing trespassing conspecifics on the social dominance, territory quality and fighting capabilities of the signaler

Night Shift: Expansion of Temporal Niche Use Following Reductions in Predator Density

Predation shapes many fundamental aspects of ecology. Uncertainty remains, however, about whether predators can influence patterns of temporal niche construction at ecologically relevant timescales. Partitioning of time is an important mechanism by which prey avoid interactions with predators. However, the traits that control a prey organism's capacity to operate during a particular portion of the diel cycle are diverse and complex. Thus, diel prey niches are often assumed to be relatively unlikely to respond to changes in predation risk at short timescales. Here we present evidence to the contrary. We report results that suggest that the anthropogenic depletion of daytime active predators (species that are either diurnal or cathemeral) in a coral reef ecosystem is associated with rapid temporal niche expansions in a multi-species assemblage of nocturnal prey fishes. Diurnal comparisons of nocturnal prey fish abundance in predator rich and predator depleted reefs at two atolls revealed that nocturnal fish were approximately six (biomass) and eight (density) times more common during the day on predator depleted reefs. Amongst these, the prey species that likely were the most specialized for nocturnal living, and thus the most vulnerable to predation (i.e. those with greatest eye size to body length ratio), showed the strongest diurnal increases at sites where daytime active predators were rare. While we were unable to determine whether these observed increases in diurnal abundance by nocturnal prey were the result of a numerical or behavioral response, either effect could be ecologically significant. These results raise the possibility that predation may play an important role in regulating the partitioning of time by prey and that anthropogenic depletions of predators may be capable of causing rapid changes to key properties of temporal community architecture

Adaptation in the optical properties of the crystalline lens in the eyes of the Lessepsian migrant Siganus rivulatus

Vision is an important source of information for many animals. The crystalline lens plays a central role in the visual pathway and hence the ecology of fishes. In this study, we tested whether the different light regimes in the Mediterranean and Red Seas have an effect on the optical properties of the lenses in the rivulated rabbitfish, Siganus rivulatus. This species has migrated through the Suez Canal from the Red Sea and established a vital population in the Mediterranean Sea. Longitudinal spherical aberration curves and focal lengths of the fish lenses were measured by laser scans and compared between the two populations. In addition, rivulated rabbitfish from the Mediterranean Sea were exposed to colored light (yellow, green and blue) and unfiltered light for periods of 1 or 13. days to test for short-term adjustments. Lens focal length was significantly longer (3%) in the Rea Sea population. The shorter focal length of the Mediterranean population can be explained as an adaptation to the dimmer light environment, as this difference makes the Mediterranean eyes 5% more sensitive than the eyes of the Red Sea population. The difference may be due to genetic differences or, more likely, adaptive developmental plasticity. Short-term regulatory mechanisms do not seem to be involved

Comparing the consequences of natural selection, adaptive phenotypic plasticity, and matching habitat choice for phenotype-environment matching, population genetic structure, and reproductive isolation in meta-populations

Organisms commonly experience significant spatiotemporal variation in their environments. In response to such heterogeneity, different mechanisms may act that enhance ecological performance locally. However, depending on the nature of the mechanism involved, the consequences for populations may differ greatly. Building on a previous model that investigated the conditions under which different adaptive mechanisms (co)evolve, this study compares the ecological and evolutionary population consequences of three very different responses to environmental heterogeneity: matching habitat choice (directed gene flow), adaptive plasticity (associated with random gene flow), and divergent natural selection. Using individual-based simulations, we show that matching habitat choice can have a greater adaptive potential than plasticity or natural selection: it allows for local adaptation while protecting genetic polymorphism despite global mating or strong environmental changes. Our simulations further reveal that increasing environmental fluctuations and unpredictability generally favor the emergence of specialist genotypes but that matching habitat choice is better at preventing local maladaptation by individuals. This confirms that matching habitat choice can speed up the genetic divergence among populations, cause indirect assortative mating via spatial clustering, and hence even facilitate sympatric speciation. This study highlights the potential importance of directed dispersal in local adaptation and speciation, stresses the difficulty of deriving its operation from nonexperimental observational data alone, and helps define a set of ecological conditions which should favor its emergence and subsequent detection in nature

Education, Migration and Source Community Incomes in Rural China

Residents in rural China doubt the benefits from education, yet there is empirical evidence supporting positive effects in urban and rural areas. This paper investigates whether education affects a variety of income attainment indicators for households in rural China, using a household survey from the provinces of Hebei and Liaoning. The analysis estimates education effects for household residents, but also for temporary migrants (rural-urban migrants) and children who have moved permanently (rural-rural migrants). This can help to answer a set of three related questions: 1) Does household welfare in rural China depend on education? 2) Is the effect of education contingent on the decision to migrate? and 3) Does education have dissimilar effect for rural-urban and rural-rural migrants? The results support that education has positive income effects and that migration yields no additional payoffs. However, there is no evidence that households benefit from higher education if migration is only temporary. Altogether, this signals positive payoffs of educational expenses to rural households but households which consider sending a migrant into the urban labor force are better off if the more educated stay at home

Who Benefits from More Housing? : A Panel Data Study on the Role of Housing in the Intermunicipal Migration of Different Age Cohorts in Sweden

Although Swedish housing standards are high and young adults leave the parental home relatively early, there are indications that for certain groups housing has, in recent years, become less accessible. We analyse how housing characteristics affect intermunicipal mobility for different age cohorts and estimate a panel data gravity model that models migration as a function of origin and destination characteristics. The results suggest that new construction in the past two decades has negatively affected migration within commuting regions more than migration between commuting regions. For metropolitan areas, there are considerable negative effects on net migration from other commuter regions because new construction has not kept pace with population growth. The effects are stronger for young adults (20-44) compared to older adults (45-74). Further, we find that, while new construction stimulates mobility for all age cohorts, the estimated relationship is weaker for the youngest adults; indicating a need for more variation in new construction to satisfy different needs. Also, we find that the decreased share of rentals since 1992 have negatively affected the short-distance mobility of the youngest adults while the effect is weaker or even positive for the remaining age cohorts

Economics of Migration

Abstract Population movements are more substantial today than at any other point in human history. If managed effectively, migration can be beneficial for all aspects of social and economic life. This thesis contains four papers, all of which are related to the economic consequences and determinants of migration, within and across countries. The first paper employs a household survey to explore whether education has an effect on the income attainments of rural households in China. The educational levels of people residing in the households and people who have moved from the households (migrants) are considered. A substantial flow of rural-urban migration, considerable drop-out rates and emerging evidence of the positive effects of education in China motivate the study. The findings generally show that the effects of education are positive. For household members, more education increases earnings from non-farm work. Permanent migrants with 7-9 years of schooling remit more money to the households than permanent migrants with 1-6 years of education. However, although temporary migrants are found to contribute to household incomes by bringing home money earned from non-farm work, the results do not indicate that more education increases the ability to do so. The second paper employs a household survey from Guatemala. Building on the general observation that distinct segments of the labor market are characterized by varying entry and exit conditions, the aim is to compare the effects of time in different segments of the labor market and to investigate whether the effects vary between migrants and natives. A particular focus lies on the dichotomous division between the informal and formal sectors. The labor market is divided into Agriculture (informal), Self-employment (informal), Uncovered Wage Work (informal) and Covered Wage Work (formal). This paper investigates how the amount of time individuals have spent at their current residence before obtaining their current job (YearsCurrent) has affected their probability of employment, and how the number of years of employment (Experience) affects earnings. Amongst other things, time can be a proxy for individual influence and knowledge. For all sectors except agriculture, it is found that YearsCurrent is positively correlated with the probability of employment, and that the effect is higher for migrants than natives. There is a reversed pattern in agriculture. Experience positively affects earnings for all covered wage workers, and there is a positive effect for migrants performing uncovered wage work. Experience has a negative correlation with earnings in agriculture for all workers. Two important findings are: 1) For natives, YearsCurrent has the strongest effect for uncovered wage workers, which could indicate a higher importance of social capital than in other sectors. 2) Migrants generally benefit more from time than natives, which contradicts migrant discrimination. The third paper employs macroeconomic data and simulates dynamic multiplier effects of international remittances in a panel of 120 countries for the period 1980 to 2006. Three structural equations are estimated to assess how a unit increase in remittances affects total income in the receiving country within one year (short run) and ten years (long run). When remittances are assumed to have the same spending patterns as other incomes (GDP), the findings suggest positive multiplier effects, which vary substantially across regions and income categories. North Africa and the Middle East and Latin America and the Caribbean had the greatest rise in income due to remittances since the 1980s (400 US$/Capita/Year). Among income categories, lower middle income economies benefited the most (330 US$/Capita/Year). Separating remittances from other incomes and allowing different spending patterns change the results quite dramatically. The results of this exercise, which must be interpreted very cautiously, suggest considerably different multiplier effects that are lower in some regions (sometimes even negative) and higher in others. The fourth paper, co-authored with Fredrik NG Andersson, explores the reverse causality problem of remittances in a new-fangled way; i.e. by testing the validity of two hypotheses about the determinants of remittances i.e. the altruism and insurance hypotheses. These predict the same short run, but different long run relationships between remittances and consumption. The hypotheses are tested by decomposing the data into cycles, representing the short run, and a trend, representing the long run. A macroeconomic panel with consumption and remittances data for 50 low and middle income economies between 1980 and 2006 is used for this purpose. This paper estimates Keynesian consumption functions with GDP and remittances per capita as explanatory variables for the full panel and for different sub panels: Declining economies, Rapidly Growing Economies, Low Income Economies and Middle Income Economies. Generally, the results provide more support for the altruism hypothesis than the insurance hypothesis

Risk assessment: to surface water in Kallerstadsdiket and Stångån near the closed Kallerstad landfill, Linköping.

Kallerstaddeponin användes aktivt för deponering av avfall mellan 1950 och 1973. Nedlagda deponier bör dock bedömas med avseende på den risk de utgör för miljö och hälsa. I denna studie, jämfördes nivåerna av zink, nickel, arsenik, koppar, ammoniak, TOT-N och TOC i deponins huvudrecipient, Kallerstadsdiket, med de gränsvärden som fastställts av Havs- och vattenmyndigheten. Därefter uppskattades Kallerstaddeponins direkta bidrag till föroreningsnivån. Slutligen, beräknades spridningsrisken, nämligen den föroreningsbelastning som flödar från Kallerstadsdiket till Stångån, som är en andra recipient. Zink, nickel och koppar visade låga nivåer och låg risk på alla provtagningsstationer. Ammoniak och arsenik visade högre nivåer och en potentiell risk för negativa effekter. Detta innebär att Kallerstadsdikets ytvatten inte klassificeras att uppnå "bra" status, även om den direkta rollen som Kallerstaddeponin spelar är tveksam i detta fall. Beräkningarna tyder på att Kallerstaddeponin tillför arsenik och TOC till föroreningsnivåerna, även om det är i små mängder. Risken för spridning av föroreningar till Stångån uppskattades vara låg. Utspädningsfaktorn uppskattades till att vara 1:320 och de ytterligare föroreningsnivåerna som härstammar från Kallerstadsdiket är låga i förhållande till de uppmätta nivåerna i Stångån. Den aktuella studien har många osäkerheter som huvudsakligen är relaterade till tillgängligheten av data. Det rekommenderas därför att tillämpa en mer fullständig provtagning med lämpliga parametrar (t.ex. pH, DOC, Ca och temperatur) i alla provtagningsstationer. Helst skulle det vara önskvärt med provtagning varje vecka under en period av ett år och sedan åter bedöma risken för att få en mer tillförlitlig uppskattning av deponins bidrag.Kallerstad landfill was in use between 1950 and 1973. Nonetheless, assessment of closed landfills and their risk to the environment and health is required. Firstly, the levels of zinc, nickel, arsenic, copper, ammonia, TOT-N and TOC in the surface water of the main recipient Kallerstadsdiket, were compared to cut-off levels given by the Swedish Agency for Marine and Water Management. Then, the direct contribution of Kallerstad landfill to the contamination level was estimated. Finally, the contamination load that flows from Kallerstadsdiket to Stångån, which is a second recipient with high natural value, was estimated. Zinc, nickel and copper showed low levels and low risk at all sampling stations. Ammonia and arsenic showed higher levels and a potential risk of adverse effects. As a result, the surface water in Kallerstadsdiket could not be classified to reach ‘good’ status, although the direct role that Kallerstad landfill plays is doubtful. Calculations suggest that Kallerstad landfill does add arsenic and TOC to the contamination levels, although in small amounts. The risk of spread of contaminants to Stångån was estimated to be low. The additional contamination levels stemming from Kallerstadsdiket are lower than the levels measured in Stångån. The dilution factor was estimated to be 1:320. Nevertheless, the current study has many uncertainties that are mainly related to data availability. It is therefore recommended to apply a more complete sampling scheme with the appropriate parameters (e.g., pH, DOC, Ca, and temperature) in all sampling stations. Ideally it would be plausible to sample every week for a period of a year and then reassess the risk, as well as to get a more reliable approximation of the contribution of the landfill itself