Hinrich Martin Schaefer

Why are fruits colorful? The relative importance of achromatic and chromatic contrasts for detection by birds

The colors of fruits and flowers are traditionally viewed as an adaptation to increase the detectability of plant organs to animal vectors. The detectability of visual signals increases with increasing contrasts between target and background. Contrasts consist of a chromatic aspect (color) and an achromatic aspect (light intensity), which are perceived separately by animals. To evaluate the relative importance of fruits’ chromatic and achromatic contrasts for the detection by avian fruit consumers we conducted an experiment with artificial fruits of four different colors in a tropical forest. We displayed the fruits against two different backgrounds, an artificial background and a natural one, because they differed in achromatic properties. We found no effect of the type of background on fruit detection rates. Detection rates differed for the four fruit colors. The probability of detection was explained by the chromatic contrast between fruits and their background, not by the achromatic contrasts. We suggest that birds attend primarily to chromatic contrast probably because these are more reliably detected under variable light conditions. Consistent with this hypothesis, we found habitat-specific differences in the conspicuousness of natural fruit colors in the study area. Fruits of understory species that are subjected to the variable light conditions within a forest displayed higher chromatic contrasts than species growing in the open restinga forest with constant bright illumination. There was no such difference for achromatic contrasts. In sum, we suggest that fruit colors differ between habitats because fruit colors that have strong chromatic contrasts against background can increase plants’ reproductive success, particularly under variable light conditions.

Bloodmeal analysis reveals avian Plasmodium infections and broad host preferences of Culicoides (Diptera: Ceratopogonidae) vectors.

Changing environmental conditions and human encroachment on natural habitats bring human populations closer to novel sources of parasites, which might then develop into new emerging diseases. Diseases transmitted by host generalist vectors are of special interest due to their capacity to move pathogens into novel hosts. We hypothesize that humans using forests for recreation are exposed to a broad range of parasites from wild animals and their vectors. A corollary of this is that new vector-host, parasite-host, and vector-parasite associations could eventually develop. Thus, we expect to observe atypical vector-host associations. Using molecular bloodmeal analysis via amplification of the mtDNA COI gene we identified the vertebrate hosts of Culicoides (Diptera: Ceratopogonidae) species in a sub-urban forest of Southwestern Germany. Bloodmeals were also checked for haemosporidian infections by amplifying a fragment of the mtDNA cyt b gene. We identified a total of 20 Culicoides species, thirteen of which fed on humans. From 105 screened bloodmeals we obtained high quality sequences for 77 samples, 73 (94.8%) originated from humans, two from livestock (Bos taurus and Equus caballus), and two from wild birds (Sylvia atricapilla and Turdus merula). We found that four Culicoides species previously assumed to feed exclusively on either birds (C. kibunensis) or domestic mammals (C. chiopterus, C. deltus, C. scoticus) fed also on humans. A total of six Culicoides abdomens were infected with avian haemosporidian parasites (Plasmodium or Haemoproteus), four of those abdomens contained blood derived from humans. Our results suggest that parasites of wild animals may be transferred to humans through infectious bites of Culicoides vectors. Further, we show that Culicoides vectors believed to be a specialist on specific vertebrate groups can have plastic feeding preferences, and that Culicoides are susceptible to infection by Plasmodium parasites, though vector viability must still be experimentally demonstrated.

Prevalence, diversity, and interaction patterns of avian haemosporidians in a four-year study of blackcaps in a migratory divide.

Migratory birds contribute to the movement of avian parasites between distant locations, thereby influencing parasite distribution and ecology. Here we analyse the prevalence, diversity and interaction patterns of Haemosporida parasites infecting Blackcap (Sylvia atricapilla) populations in a recently established migratory divide of southwestern Germany across 4 years. We hypothesize that the temporal and spatial isolation provided by 2 sympatric Blackcap breeding populations (migratory divide) might modify ecological interactions and thus create differences in the structure of the parasite community according to migratory route. We used a fragment of the mitochondrial DNA cytochrome b gene to determine haemosporidian haplotypes. We detected an overall infection prevalence of 70.3% (348 out of 495 blackcaps sampled from 2006 to 2009), and prevalence rates were significantly different among years and seasons. We observed a total of 27 parasite haplotypes infecting blackcaps, from them 6 new rare Haemoproteus haplotypes were found in 2 mixed infections. H. parabelopolskyi haplotypes SYAT01 (35.7%) and SYAT02 (20.8%) comprised most of the infections. An association analysis suggests that SYAT01 and SYAT02 are interacting negatively, implying that they are either competing directly for host resources, or indirectly by eliciting a cross-immune response. Molecular data show no clear difference between the parasite communities infecting blackcaps with different migratory routes, despite some temporal and spatial isolation between the two sympatric blackcap populations.

Reproductive success depends on the quality of helpers in the endangered, cooperative El Oro parakeet (Pyrrhura orcesi)

In cooperative species, helping behaviour and reproductive success can be correlated, but understanding this correlation is often impaired by the difficulty to correctly infer causation. While helpers can incur costs by participating in brood care, it is yet unclear if their help depends on their individual quality. We address these questions in the previously unknown cooperative breeding system of the endangered El Oro parakeet (Pyrrhura orcesi). Specifically, we ask (i) whether breeders benefit directly from helpers by an enhanced reproductive success and if so, (ii) whether the amount of this potential benefit is regulated by the quality of contributing group members. Groups consist of a dominant breeding pair accompanied by helpers, but cooperation is not obligate. Microsatellite heterozygosity was used to assess individual quality; its suitability as indicator of quality was reflected in the positive relationship between offspring heterozygosity and recruitment into the population. The reproductive success of breeding pairs depended on helper (genetic) quality and the number of helpers. This relationship occurred on two different levels: clutch size and fledging success, indicating (i) that females profit from high‐quality helpers and probably adjust clutch size accordingly and (ii) that the helpers increase fledging success. Congruently, we found that offspring body condition is positively affected by helper quality, which is most probably explained by the increased feeding rates when helpers are present. We suggest a causal link between cooperation and reproductive success in this frugivorous, endangered parakeet. Further, helper (genetic) quality can be a relevant factor for determining reproductive fitness in cooperative species, particularly in small and bottlenecked populations.

Spatial behaviour in the Aquatic Warbler (Acrocephalus paludicola) during mating and breeding@@@Räumliches Verhalten des Seggenrohrsängers (Acrocephalus paludicola) während Partnerfindung und Bebrütung

The range use of both sexes of the Aquatic Warbler was studied during two breeding seasons by radio-tracking. Males used home ranges of up to 8 ha. These home ranges over-lapped by up to 74 %, (mean 51 %) between individuals. During the mating period and prior to nesting, females used isolated sites of 2.8 to 6.4 ha (mean: 4.2 ha) within activity ranges of 100 to 160 ha (mean: 120 ha). Home ranges of different females overlapped by up to 20 %. However, during nest-building and incubation, the average size of home ranges in females was only 1.6 ha. Since no constant ranges were observed, we conclude that Aquatic Warblers are not territorial in the breeding season. In zwei aufeinanderfolgenden Brutzeiten wurde die Raumnutzung von Seggenrohrsängern mittels Telemetrie untersucht. Die ermittelte Größe der Streifgebiete von Männchen betrug in der gesamten Brutzeit bis zu 8 ha. In dem Streifgebiet eines einzelnen Männchens wurden bis zu elf telemetrierte Männchen festgestellt. Die Überlappungen der Streifgebiete telemetrierter Männchen betrugen durchschnittlich 51 %, maximal 74 %. Weibchen nutzten während der Paarungszeit nicht zusammenhängende inselartige Areale von insgesamt 2,8 bis 6,4 ha (Mittelwert 4,2 ha) innerhalb von Aktionsräumen von 110 bis 160 ha (Mittelwert 120 ha). Diese Areale überlappten zu 20 % mit den Aufenthaltsgebieten anderer Weibchen. Während des Brütens sank die Größe der Streifgebiete der Weibchen auf durchschnittlich 1,6 ha. Da im Beobachtungszeitraum keine konstant genutzten Aufenthaltsgebiete vorlagen, schließen wir, daß sich Seggenrohrsänger in der Brutzeit nicht territorial verhalten.

Feeding strategies and food intake of Blackcaps (Sylvia atricapilla) consuming ripe or unripe fruits and insects@@@Ernährungsstrategien und Nahrungsaufnahme von Mönchsgrasmücken (Sylvia atricapilla) bei reifen oder unreifen Holunderbeeren sowie Insekten

We compared the feeding behaviour of two groups of captive Blackcaps (Sylvia atricapilla) on a mixed diet consisting of an insect diet and ripe or unripe fruits. Unripe Black Elder (Sambucus nigra) fruits have lower nutritional values, especially for protein, than ripe fruits. We tested the non exclusive hypotheses that birds increase their food intake and/or their digestive efficiencies when feeding on the low quality resource of unripe fruits. Birds fed readily on unripe fruits even when the insect diet was providedad libitum. With respect to food intake, birds consuming unripe fruits always had a lower fruit intake and higher intake of the insect diet than birds feeding on ripe fruits. Thus, the intake of unripe fruits is constrained, probably owing to the accumulation of deterrent fruit compounds. When the insect diet was reduced to 45 % of the birds’ad libitum intake, individuals consuming unripe fruits lost 5 % body mass, while those consuming ripe fruits maintained constant body mass. The mean difference in daily gross caloric intake between the two groups was only 4 kJ. Differences in body mass development are explainable by the different digestibility of ripe and unripe fruits. At the same caloric gross intake, birds feeding for 12 days on unripe fruits lost less body mass (5 %) than birds feeding newly on unripe fruits (16 %). We suggest that an increase in digestive efficiencies of birds being accustomed to this diet causes the difference in body mass development. Der Verzehr unreifer Früchte durch frugivore Vögel ist v. a. in Zeiten von Nahrungsknappheil beobachtet worden. Wir untersuchten die Ernährungsstrategien von zwei Gruppen von Mönchsgrasmücken, die sich von einem gemischtem Futter bestehend aus einem Insektenfutter und unreifen oder reifen schwarzen Holunderbeeren (Sambucus nigra) ernährten. Reife Früchte des schwarzen Holunders haben einen höheren Nährstoffgehalt als unreife Beeren, dies betrifft v. a. den Proteingehalt. Es wurden zwei sich nicht ausschließende Hypothesen getestet, dass Vögel entweder ihre Nahrungsaufnahme und/oder ihre Nahrungsverwertung erhöhen, wenn sie sich von unreifen Früchten als qualitativ geringe Futterquelle ernähren. Die Vögel fraßen unreife Früchte auch, wenn das zusätzliche Insektenfutterad libitum zur Verfügung stand. Vögel, die unreife Früchte fraßen, nahmen in je dem Versuchsstadium weniger Früchte und mehr Insektenfutter auf als diejenigen, die sich von reifen Früchten ernährten. Die Aufnahme unreifer Früchte ist wahrscheinlich durch die schnelle Akkumulation belastender sekundärer Pflanzenstoffe eingeschränkt, die den Konsum von unreifen Früchten verhindern sollen. Bei der Reduktion des zusätzlichen Insektenfutters auf 45 % derad libitum Aufnahme, verlor die Gruppe, die sich von unreifen Früchten ernährte, 5 % Gewicht über vier Tage, während Vögel, die reife Früchte fraßen, ihr Gewicht hielten. Dabei nahmen Individuen der letzten Gruppe durchschnittlich nur 4 kJ mehr pro Tag auf als Vögel der anderen Gruppe. Die unterschiedliche Gewichtsentwicklung ist durch Unterschiede in der Verwertung reifer und unreifer Früchte erklärbar. An unreife Früchte gewöhnte Vögel verloren weniger Gewicht (5 %) bei einem Futter, das weitgehend aus unreifen Früchten bestand, als Vögel, die zum ersten Mal mit unreifen Früchten gefüttert wurden (16 %). Da sich die Energie- und Nährstoffaufnahme während und vor dem Vergleich beider Gruppen nicht unterschied, nehmen wir an, dass eine erhöhte Verdauungseffizienz die unterschiedliche Gewichtsentwicklung bedingt.

Limited Dispersal and Significant Fine - Scale Genetic Structure in a Tropical Montane Parrot Species

Tropical montane ecosystems are biodiversity hotspots harbouring many endemics that are confined to specific habitat types within narrow altitudinal ranges. While deforestation put these ecosystems under threat, we still lack knowledge about how heterogeneous environments like the montane tropics promote population connectivity and persistence. We investigated the fine-scale genetic structure of the two largest subpopulations of the endangered El Oro parakeet (Pyrrhura orcesi) endemic to the Ecuadorian Andes. Specifically, we assessed the genetic divergence between three sites separated by small geographic distances but characterized by a heterogeneous habitat structure. Although geographical distances between sites are small (3–17 km), we found genetic differentiation between all sites. Even though dispersal capacity is generally high in parrots, our findings indicate that dispersal is limited even on this small geographic scale. Individual genotype assignment revealed similar genetic divergence across a valley (~ 3 km distance) compared to a continuous mountain range (~ 13 km distance). Our findings suggest that geographic barriers promote genetic divergence even on small spatial scales in this endangered endemic species. These results may have important implications for many other threatened and endemic species, particularly given the upslope shift of species predicted from climate change.