The environmental determinants of the insular butterfly faunas of the British Isles

Pathogens can exert strong selective forces upon host populations. However, before we can make any predictions about the consequences of pathogen-mediated selection, we first need to determine whether patterns of pathogen distribution are consistent over spatiotemporal scales. We used molecular techniques to screen for a variety of blood pathogens (avian malaria, pox and trypanosomes) over a three-year time period across 13 island populations of the Berthelot's pipit (Anthus berthelotii). This species has only recently dispersed across its range in the North Atlantic, with little subsequent migration, providing an ideal opportunity to examine the causes and effects of pathogenic infection in populations in the early stages of differentiation. We screened 832 individuals, and identified two strains of Plasmodium, four strains of Leucocytozoon, and one pox strain. We found strong differences in pathogen prevalence across populations, ranging from 0 to 65%, and while some fluctuations in prevalence occurred, these differences were largely stable over the time period studied. Smaller, more isolated islands harboured fewer pathogen strains than larger, less isolated islands, indicating that at the population level, colonization and extinction play an important role in determining pathogen distribution. Individual-level analyses confirmed the island effect, and also revealed a positive association between Plasmodium and pox infection, which could have arisen due to dual transmission of the pathogens by the same vectors, or because one pathogen lowers resistance to the other. Our findings, combined with an effect of infection on host body condition, suggest that Berthelot's pipits are subject to different levels of pathogen-mediated selection both across and within populations, and that these selective pressures are consistent over time.

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“…As some islands had no pathogens, n ? 1 was used for pathogen species richness (Cornell 1986;Hockin 1981).…”

Section: Statistical Analysesmentioning

confidence: 99%

Biogeographical patterns and co-occurrence of pathogenic infection across island populations of Berthelot’s pipit (Anthus berthelotii)

et al. 2011

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“…One inherent problem is that S has no value for A=0. This can be remedied by modifying the exponential relationship using log(S+1) instead of log S, as shown by Hockin (1981), McGuinness (1984), Cornell (1986) and Williams (1996). Another way to satisfy this problem is to substitute log A with log(1+A).…”

Section: Function Models and Graphic Calculationsmentioning

confidence: 99%

Habitat size and number in multi‐habitat landscapes: a model approach based on species‐area curves

Tjørve¹

2002

Ecography

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This paper discusses species diversity in simple multi‐habitat environments. Its main purpose is to present simple mathematical and graphical models on how landscape patterns affect species numbers. The idea is to build models of species diversity in multi‐habitat landscapes by combining species‐area curves for different habitats. Predictions are made about how variables such as species richness and species overlap between habitats influence the proportion of the total landscape each habitat should constitute, and how many habitats it should be divided into in order to be able to sustain the maximal number of species. Habitat size and numbers are the only factors discussed here, not habitat spatial patterns. Among the predictions are: 1) where there are differences in species diversity between habitats, optimal landscape patterns contain larger proportions of species rich habitats. 2) Species overlap between habitats shifts the optimum further towards larger proportions of species rich habitat types. 3) Species overlap also shifts the optimum towards fewer habitat types. 4) Species diversity in landscapes with large species overlap is more resistant to changes in landscape (or reserve) size. This type of model approach can produce theories useful to nature and landscape management in general, and the design of nature reserves and national parks in particular.

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“…As another example of the application of the EVF model, this time in the context of multiple regression, I re-analyzed Hockin's (1981) data on numbers of butterfly species on islands in the British Isles. Hockin concluded that island area, distance of the island from the mainland (Britain), and the number of butterfly species breeding within a 25-km radius of the nearest point of the mainland were the principal determinants of the number of species regularly breeding on each island.…”

Section: Comparison Of the Power And Evf Models Of The Species-area Rmentioning

confidence: 99%

An Extreme‐Value Function Model of the Species Incidence and Species‐‐Area Relations

Williams

1995

Ecology

103

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The power function model S = CAz of the species—area relation has a number of shortcomings: it is unbounded, is unable to deal with islands with zero species, and is inappropriate to the known sampling distribution of S. Using only the null assumption that species are randomly allocated to areas, I propose an extreme—value function (EVF) model of the species—area relation derived from Coleman's theory of random placement. This model accords with empirical and theoretical results that have called into question the accuracy of the power function model at large areas, and resolves two dilemmas in the power function model: the lack of any bound to species number, and heteroscedasticity in the sampling distribution of species number. The model is also able to deal with islands with zero species, without modification. The EVF is comparable to the power function model over most practical ranges of island sizes, but has properties that make it superior to the power function model. The EVF model also provides a logical synthesis of single—species incidence and multiple—species models, and as a model of single—species incidence has parameters with biological meaning.

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The environmental determinants of the insular butterfly faunas of the British Isles

Cited by 11 publications

References 14 publications

Biogeographical patterns and co-occurrence of pathogenic infection across island populations of Berthelot’s pipit (Anthus berthelotii)

Biogeographical patterns and co-occurrence of pathogenic infection across island populations of Berthelot’s pipit (Anthus berthelotii)

Habitat size and number in multi‐habitat landscapes: a model approach based on species‐area curves

An Extreme‐Value Function Model of the Species Incidence and Species‐‐Area Relations

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