The devastation of island faunas by alien species has been instrumental in raising concerns about the global threat to biological diversity. Colonial nesting species, often restricted to islands, have been affected severely. Eradication of introduced species as a means to alleviate the problem is usually done with little or no understanding of the mechanisms governing interactions between introduced and native species. Such an understanding could help target management action. We analyzed how island area, rock substrate, bird species biology, and presence of an introduced species, the black rat ( Rattus rattus), interact to explain the distribution and abundance of colonial nesting birds on a set of 72 islands from six archipelagos in the western Mediterranean. Rats were introduced to this region over 2000 years ago, and these communities have had time to reach an equilibrium. Using general linear models, we show that rats have affected species distributions more on the smaller islands and on islands with an acidic or neutral rock substrate; larger bird species are more resistant. On the smaller islands, where rat densities are highest, larger colonial birds are negatively affected. On larger islands, where rat densities are lower and fluctuate form year to year, larger colonial birds can maintain healthy populations despite the presence of rats. Although rats caused local extinction or reduction in bird abundance, the presence of islands varying in size and/or substrate allowed most archipelagos to retain their suite of colonial nesting bird species, despite a presumably reduced abundance for most species.
Todiramphus chloris is the most widely distributed of the Pacific's ‘great speciators’. Its 50 subspecies constitute a species complex that is distributed over 16 000 km from the Red Sea to Polynesia. We present, to our knowledge, the first comprehensive molecular phylogeny of this enigmatic radiation of kingfishers. Ten Pacific Todiramphus species are embedded within the T. chloris complex, rendering it paraphyletic. Among these is a radiation of five species from the remote islands of Eastern Polynesian, as well as the widespread migratory taxon, Todiramphus sanctus. Our results offer strong support that Pacific Todiramphus, including T. chloris, underwent an extensive range expansion and diversification less than 1 Ma. Multiple instances of secondary sympatry have accumulated in this group, despite its recent origin, including on Australia and oceanic islands in Palau, Vanuatu and the Solomon Islands. Significant ecomorphological and behavioural differences exist between secondarily sympatric lineages, which suggest that pre-mating isolating mechanisms were achieved rapidly during diversification. We found evidence for complex biogeographic patterns, including a novel phylogeographic break in the eastern Solomon Islands that separates a Northern Melanesian clade from Polynesian taxa. In light of our results, we discuss systematic relationships of Todiramphus and propose an updated taxonomy. This paper contributes to our understanding of avian diversification and assembly on islands, and to the systematics of a classically polytypic species complex.
Summary 1.Understanding how density-dependent and independent processes influence demographic parameters, and hence regulate population size, is fundamental within population ecology. We investigated density dependence in growth rate and fecundity in a recovering population of a semicolonial raptor, the osprey Pandion haliaetus [Linnaeus, 1758], using 31 years of count and demographic data in Corsica. 2. The study population increased from three pairs in 1974 to an average of 22 pairs in the late 1990s, with two distinct phases during the recovery (increase followed by stability) and contrasted trends in breeding parameters in each phase. 3. We show density dependence in population growth rate in the second phase, indicating that the stabilized population was regulated. We also show density dependence in productivity (fledging success between years and hatching success within years). 4. Using long-term data on behavioural interactions at nest sites, and on diet and fish provisioning rate, we evaluated two possible mechanisms of density dependence in productivity, food depletion and behavioural interference. 5. As density increased, both provisioning rate and the size of prey increased, contrary to predictions of a food-depletion mechanism. In the time series, a reduction in fledging success coincided with an increase in the number of non-breeders. Hatching success decreased with increasing local density and frequency of interactions with conspecifics, suggesting that behavioural interference was influencing hatching success. 6. Our study shows that, taking into account the role of non-breeders, in particular in species or populations where there are many floaters and where competition for nest sites is intense, can improve our understanding of density-dependent processes and help conservation actions.
Long‐lived species show delayed maturity and generally skip breeding sites on a given year, causing difficulties in estimating demographic parameters. A novel multi‐state capture – recapture model (model G for general) is proposed to estimate survival and recruitment. Model G considers long and short periods of non‐attendance at the breeding site. Model G is compared against a reduced model (model R) to test if pre‐breeders skip the studied site a given year, potentially prospecting other breeding habitats. This model is applied to the vulnerable Cory's shearwaters seabird species. As for many species, natal philopatry, pre‐breeding attendance and prospecting play an important role for recruitment into the breeding population. Model G shows that all Cory's shearwaters come back to their natal colony, and attend the colony before recruiting into the breeding population. Moreover, model G is preferred against model R, highlighting that prospecting plays a potentially role in the recruitment processes. Return and recruitment probabilities show similar time variation, suggesting an environmental forcing. The maximum probability of the first breeding is reached at the age of seven years. During the first year the annual survival rate is 0.52 (IC95%=[0.40, 0.64]) and pre‐breeders and adult annual survival rates do not differ, being respectively 0.88, IC95%=[0.83, 0.92] and 0.89, IC95%=[0.88, 0.9]. Model G provides an improvement to estimate demographic parameters for long‐lived species life cycle and an adequate framework to test the influence of covariates. Model G is structured by age and breeding status categories, allowing easy further population models.
Aim Deciphering the complex colonization history of island archipelagos is greatly facilitated by comprehensive phylogenies. In this study we investigate the phylogeny and biogeography of the insular reed-warblers (genus Acrocephalus) of the tropical Pacific Ocean, from Australia to eastern Polynesia.Location Oceania.Methods We used sequences of mitochondrial DNA (cytochrome b, ND2 and ATP8 genes) to infer the colonization patterns of reed-warblers endemic to Pacific islands and Australia. We sampled all known taxa of Acrocephalus in the Pacific except A. luscinius nijoi, for which no sample was available. Most taxa were represented by toe-pad samples from museum specimens collected in the 19th and 20th centuries. With a few exceptions, several specimens per taxon were sequenced independently in two institutions (Smithsonian Institution and Natural History Museum of Geneva).Results Our data indicate that Pacific reed-warblers do not form a monophyletic group, because A. luscinius luscinius from Guam falls outside the main Pacific radiation. The remaining Pacific taxa are divided into two clades: one clade includes all the reed-warblers from Micronesia (except Guam) and Australia, and two Polynesian taxa from the Line Islands and the southern Marquesas; the other clade includes all remaining Polynesian taxa. The taxa endemic to three archipelagos (Mariana, Marquesas and Society islands) are polyphyletic, suggesting several independent colonizations. Main conclusions Our results provide evidence for a complex pattern of colonization of the Pacific by reed-warblers. Calibration analyses suggest that reed-warbler lineages are much younger than the ages of the islands they occupy. Several remote archipelagos were colonized independently more than once. Consequently, we infer that the colonization of reed-warblers in the Pacific did not follow a regular, stepping-stone-like pattern. The phylogeny also suggests a previously undetected case of reverse colonization (from island to continent) for the Australian lineage and indicates that A. luscinius, as currently defined, is not monophyletic. We discuss the supertramp strategy of reed-warblers in the Pacific and show that, although Pacific reed-warblers meet some of the supertramp criteria in their aptitude for colonizing remote archipelagos, their life history characteristics do not fit the model.
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