Seed and microsite limitations of recruitment and the impacts of post-dispersal seed predation at the within population level

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Calviño-Cancela, M., 2007. Seed and microsite limitations of recruitment and the impacts of post-dispersal seed predation at the within population level. Plant Ecology, 192(1), pp.35-44.

Seed predation may cause important seed losses in plant populations, but its impact on the dynamics of populations will depend on the degree of seed or microsite limitations for recruitment. Seed losses will only affect recruitment if it is seed limited. The nature of recruitment limitation (seeds or microsites) is usually ascribed to whole plant populations but it may vary within populations among microhabitats and habitats. Thus, the potential impact of seed predation will also vary within the population, being highest where recruitment is seed limited. The impact to the whole population will depend on the spatial concordance between the intensity of seed predation and that of seed limitation. Recruitment limitations (with seed addition experiments), seed predation (with seed removal experiments), and the dynamics of seed availability in the soil (with soil samples taken both after seed dispersal and before the following dispersal event) of the shrub Corema album (Empetraceae) were investigated in dunes in NW Spain, at microhabitats ‘open ground’, ‘underneath C. album’, and ‘underneath C. album’ at two habitats, sparse and dense scrub. The nature of recruitment limitation (seeds vs. microsites) varied within the population. It was seed limited in the microhabitat ‘open ground’ and microsite limited under shrub cover. The spatial patterns of seedling recruitment were unrelated to seed availability but strongly affected by germination requirements. The spatial discordance between seed availability and recruitment implies a crucial constraint for processes affecting seed availability (seed predation but also e.g., dispersal) to impact recruitment. They will not affect its spatial pattern but only its quantity as long as they act in those sites selected by seeds to germinate. Seed predation was highest underneath mother plants and lowest in open ground. Thus, its potential impact is low, as it is centred where recruitment is not seed limited. This study shows that the analysis of seed predation in relation to recruitment limitations at smaller spatial scales within the population provides more insight to understand its impact.

Simplifying methods to assess site suitability for plant recruitment

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Calvino-Cancela, M., 2011. Simplifying methods to assess site suitability for plant recruitment. Plant Ecology, 212(8), pp.1375-1383.

Few studies link seed dispersal with its demographic consequences, or provide reliable estimates of seed dispersal effectiveness. One reason is the complexity of measuring the suitability for plant recruitment of seed arrival sites. In this study, I compare three methods that differ in the effort required to measure site suitability for seedling recruitment. All are based on the proportion of seeds that become seedlings (seedling-to-seed ratios). Method I is the most detailed and labour intensive. The fate of seeds was followed throughout the different steps of the recruitment process, from fruit removal until seedling emergence, including both seeds dispersed by different animals and undispersed seeds. Method II is based on seed addition experiments. Seeds were sowed in plots, and seedlings emerging were counted in the following two seasons. In Method III, average seed input during dispersal was measured with soil seed bank samples taken in pre- and post-dispersal periods, and seedling emergence estimated with samples of three seasons. Method II provided results similar to those of Method I, which, conversely, provides more insight in the actual processes driving recruitment. Method III, however, systematically underestimated site suitability (seedling-to-seed ratios) by about 50% as compared to the other methods in all microhabitats studied. Relative instead of absolute indices of site suitability were, however, reliable with this method. Method II and III are significantly less costly and could be good alternatives to Method I for some purposes, simplifying future studies on the demographic consequences of seed dispersal and the effectiveness of dispersers.

Helminth fauna of the yellow-legged gull Larus cachinnans in Galicia, north-west Spain

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Sanmartín, M.L., Cordeiro, J.A., Alvarez, M.F. and Leiro, J., 2005. Helminth fauna of the yellow-legged gull Larus cachinnans in Galicia, north-west Spain. Journal of Helminthology, 79(04), pp.361-371.

Thirty-six helminth species were found in 324 gulls examined during June 1994 to February 1996 from different localities of Galicia: 25 trematodes (Brachylaima sp., Brachylecithum microtesticulatum, Cardiocephaloides longicollis, Cryptocotyle lingua, Cryptocotyle concavum, Diplostomum spathaceum, Echinostephilla virgula, Galactosomum phalacrocoracis, Gigantobilharzia acotylea, Gymnophallus deliciosus, Gynaecotyla longiintestinata, Himasthla elongata, Himasthla quissetensis, Knipowitschiatrema nicolai, Levinseniella (Levinseniella) propinqua, Maritrema gratiosum, Maritrema linguilla, Microphallus primas, Microphallus similis, Ornithobilharzia canaliculata, Parorchis acanthus, Phagicola minuta, Psilostomum brevicolle, Renicola sp. and Stephanoprora denticulata), four cestodes (Alcataenia micracantha, Microsomacanthus ductilis, Tetrabothrius (Oriana) erostris and Wardium cirrosa), six nematodes (Anisakis simplex, Contracaecum rudolphii, Cosmocephalus obvelatus), Eucoleus contortus, Paracuaria adunca and Tetrameres (Tetrameres) skrjabini) and one acanthocephalan (Arhythmorhynchus longicollis). Tetrabothrius erostris was the most prevalent species (79.6%), followed by C. obvelatus (47.8%), C. lingua (37.4%), G deliciosus (30.9%), G. longiintestinata (22.8%), P. adunca (21.9%), B. microtesticulatum (17.6%), E. contortus (14.5%) and M. similis (9.3%). Microphallus similis was the dominant species, with a Berger-Parker index (BP) of 0.32, followed by T. erostris (BP=0.10). All species presented an aggregated dispersion except G. acotylea and G. phalacrocoracis, which showed a random dispersion. Species that seem to have the greatest predilection for specific sites along the intestine are: C. longicollis and A. micracantha (first third), Brachylaima sp., M. similis and G. longiintestinata (last third) and A. longicollis (second half). Eight species are known to be pathogenic to commercially important fish or molluscan species and several are pathogenic to humans.

Influence of host age and sex on the helminth fauna of the yellow-legged gull (Larus michahellis) in Galicia (northwestern Spain)

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Álvarez, M.F., Cordeiro, J.A., Leiro, J.M. & Sanmartín, M.L., 2006. Influence of host age and sex on the helminth fauna of the yellow-legged gull (Larus michahellis) in Galicia (northwestern Spain). Journal of Parasitology, 92(3), pp.454-458.

We studied the influence of host age and sex on the helminth fauna of 324 Larus michahellis captured in different locations in the region of Galicia (northwestern Spain). Gulls were grouped into prefledglings, first-year immature birds, second- and third-year immature birds, and adults. Second-year, third-year, and adult birds were grouped by sex. Thirty-six helminth species were recorded. Total species richness and mean infracommunity species richness were both significantly lower for prefledglings than for the other age groups. Prevalence increased significantly with age for Brachylecithum microtesticulatum, probably reflecting changing feeding habits. Likewise, 8 species (Cardiocephaloides longicollis, Microphallus similis, Maritrema gratiosum, Gynaecotyla longiintestinata, Brachylecithum microtesticulatum, Himasthla elongata, Parorchis acanthus, and Renicola sp.) were absent or had very low prevalence in prefledglings. At least 5 of these 8 species are transmitted to gulls through ingestion of molluscs or crustaceans, which suggests that these types of prey are seldom fed to prefledglings. In Gymnophallus deliciosus, G. longiintestinata, and Cosmocephalus obvelatus, mean intensity, and in the latter case prevalence, declined with age, suggesting that protective immunity against these species increase with age. Only G. deliciosus, Microphallus similis, and G. longiintestinata presented significant differences between the sexes.

On the oxidative cost of begging: antioxidants enhance vocalizations in gull chicks

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Noguera, J.C., Morales, J., Pérez, C. & Velando, A., 2010. On the oxidative cost of begging: antioxidants enhance vocalizations in gull chicks. Behavioral Ecology, 21(3), pp.479-484.

Offspring solicit food to their parents by begging displays, which are important in the parent–offspring communication. Most theoretical approximations on this behavior have centered on the view of begging as an honest signal of need or as a form of scramble competition for resources. In both signaling models, costly begging is necessary to stabilize the begging strategy at equilibrium. Nevertheless, evidence supporting begging as costly behavior remains scarce. We investigated whether oxidative stress may represent a general form of proximate cost of begging and also whether begging is related to offspring nutritional condition. To test this, we experimentally modified the chicks’ nutritional condition and vitamin E availability and measured the effects on different begging components. The intensity of all begging components increased in chicks that were intake restricted, whereas vitamin E specifically enhance the total number of chatter calls given by chicks, mainly in those with a lower body size. Our results suggest that begging behavior is an antioxidant demanding activity and support the idea that oxidative stress may be a cost of begging. Our findings also suggest that begging behavior may be an honest signal of the nutritional and oxidative status of the chicks.

Effect of testosterone on the behaviour of yellow-legged gulls (Larus cachinnans) in a high-density colony during the courtship period

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Alonso-Alvarez, C. & Velando, A., 2001. Effect of testosterone on the behaviour of yellow-legged gulls (Larus cachinnans) in a high-density colony during the courtship period. Ethology Ecology & Evolution, 13(4), pp.341-349.

Yellow-legged gulls breed in high density areas, and the condition dependent hypothesis suggests that birds with high physical condition can obtain breeding benefits in high-density areas because they are able to pay off the energetic costs of aggressive behaviour and territory defence. This study and others showed a relationship between aggressiveness or copulation behaviour and nest-density during the pre-laying period in gulls. The link between density and behaviour can be explained by the strong competition for space and mates. Testosterone regulates male behaviour and can play an important role in the condition-dependent hypothesis. We tested the effects of testosterone implants on male breeding behaviour. In a high-density colony, testosterone-implanted male yellow-legged gulls showed higher aggression and copulation frequencies than controls during the courtship period. In addition, these testosterone-treated birds acquired larger territories than the controls. Thus, a high testosterone level can increase individual fitness in densely populated areas given the benefits derived, on the one hand, from a large territory and, on the other, from an increased copulation rate that would guarantee the male’s paternity of the chicks born in his own nest. Since testosterone increases energetic requirements, only high-quality males would be able to pay off the costs of high levels of testosterone and so obtain the benefits of breeding in high-density areas. Testosterone could therefore provide a proximate mechanism regulating nest density in gull colonies.

Age-dependent changes in plasma biochemistry of yellow-legged gulls (Larus cachinnans)

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Alonso-Alvarez, C., 2005. Age-dependent changes in plasma biochemistry of yellow-legged gulls (Larus cachinnans). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 140(4), pp.512-518.

The study of avian plasma chemistry is providing useful reference values for the management of endangered and game species, supporting veterinarians in their diagnostics, and also bringing to light relevant physiological adaptations during periods of food-shortage. Age is an important source of variability for plasma chemistry. Here I report plasma chemistry of yellow-legged gulls Larus cachinnans from different ages, between post-independence and adulthood, a 5-year interval. Increase in plasma cholesterol concentration and decreases in uric acid, inorganic phosphorus and alkaline phosphatase values were seen. Body mass corrected by body size (i.e. body condition) increased with age, plasma cholesterol being positively correlated in females, but not in males. Moreover, cholesterol was also positively correlated to gonad size in both sexes. Long-term developmental changes in this species, such as gonad development and the acquisition of an optimal body mass for reproduction, could explain these findings. Finally, inorganic phosphorus and alkaline phosphatase, both traditionally related to osteogenesis, were not associated to deferred skull ossification, as originally was suggested in other species.

Effects of testosterone implants on pair behaviour during incubation in the Yellow‐legged Gull Larus cachinnans

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Alonso‐Alvarez, C., 2001. Effects of testosterone implants on pair behaviour during incubation in the Yellow‐legged Gull Larus cachinnans. Journal of Avian Biology, 32(4), pp.326-332.

The Yellow-legged Gull Larus cachinnans is monogamous with bi-parental incubation. In this study, the effects of high levels of plasma testosterone in male Yellow-legged Gulls during the incubation period were analysed. Free-living male gulls were implanted with testosterone (T-males), and their sexual behaviour within the pair was observed and compared with that of control pairs. Egg temperatures, length of incubation and hatching success were also analysed. T-males and their mates displayed more sexual behaviour than the controls. T-males engaged in mounting behaviour with their mates, whereas control males did not. Proportionally less time was spent incubating (in relation to time present in the colony) by T-males than control males. However, the mates of T-males did not spend more time incubating than control females to compensate for male neglect, although they did spend more time on the territory. Egg temperature in T-male nests was significantly lower than in control nests, but no significant difference in the length of incubation or hatching success between the two groups was found. In birds, the effects of high testosterone levels on male behaviour during incubation have only been analysed in a polyandrous species whose females usually do not contribute to incubation. The present results thus suggest that those males of a monogamous species with biparental incubation that sustain high testosterone levels after laying, thus reducing their contributions to incubation, will be confronted with a lack of compensation from their mates during incubation. Finally, this lack of female compensation seems to be mediated by behavioural interactions with the male rather than by her absence
from the colony.

Female control in yellow-legged gulls: trading paternity assurance for food

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Velando, A., 2004. Female control in yellow-legged gulls: trading paternity assurance for food. Animal Behaviour, 67(5), pp.899-907.

Females in many socially monogamous birds copulate hundreds of times more than necessary for fertilization, although little is known about the benefits of this excess. Females may not directly benefit from high copulation rates, but instead may exploit male interest in copulating to obtain benefits. In species with courtship feeding, females may trade copulations for food (immediate benefits hypothesis). I tested this hypothesis by analysing female behaviour during courtship in yellow-legged gulls, Larus cachinnans. Female gulls to some extent controlled sperm transfer, because they moved during copulation bouts, and this behaviour influenced the number of cloacal contacts per mounting that the male achieved. Female control was related to previous feeding by the male, and hence the male courtship feeding rate correlated with the cloacal contact rate. Males that give more food probably enhance their chances of fathering offspring. By analysing within-individual female behaviour, I also found that the number of cloacal contacts was higher when the male fed the female than when he did not, which indicates that female gulls followed a decision rule to resist copulation when food is not given. Overall, these results support the hypothesis that female gulls manipulate their mates to obtain food.

The evolution of multicomponent begging display in gull chicks: sibling competition and genetic variability

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Kim, S.Y., Noguera, J.C., Morales, J. & Velando, A., 2011. The evolution of multicomponent begging display in gull chicks: sibling competition and genetic variability. Animal Behaviour, 82(1), pp.113-118.

The evolution of begging display may be influenced by gene–environment interaction, through the mechanisms that adjust begging behaviour to environmental conditions of offspring, including intensity of sibling competition within broods. We decomposed the complex begging display of yellow-legged gull, Larus michahellis, chicks into two different functional components: begging for food (pecks) and drawing the attention of parents (chatter calls). We examined these begging components in 2-day-old chicks that hatched and grew up in foster nests, by performing a begging test for each chick alone without the hindrance of its foster siblings. Male chicks and those with poorer body condition begged for food at higher rates than females and those with better body condition, respectively. Chicks from larger broods begged for food more frequently, but chicks from male-biased broods begged less frequently. If begging is costly, chicks may adjust their begging efforts to the intensity of sibling competition. Frequency of chatter calls varied with sex, chick order within broods and body condition: females, the third chicks and those with poorer condition produced chatter calls more frequently. Genetic origin had a significant effect on frequency of chatter calls but not on begging for food, while foster nest effect was null in both traits. Therefore, chatter calls (but not pecks) can be subject to evolution under directional selection. Different begging components may have evolved through different evolutionary pathways.