ORIGINAL ARTICLE: The biogeography of avian extinctions on oceanic islands

Karels, Tim J.; Dobson, F. Stephen; Trevino, Heather S.; Skibiel, Amy L.

doi:10.1111/j.1365-2699.2007.01832.x

Cited by 22 publications

(36 citation statements)

References 16 publications

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“…Island endemics often have contracted ranges and population sizes, leaving them vulnerable to changes associated with human arrival and influence, as well as stochastic events (Karels et al 2008). Furthermore, small islands may lose species more quickly than large islands because of the greater scope of human influence per island area (Steadman 2006).…”

Section: Discussionmentioning

confidence: 99%

Population status, habitat dependence, and reproductive ecology of Bahama Orioles: a critically endangered synanthropic species

Price¹,

Lee²,

Hayes³

2011

Journal of Field Ornithology

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Recent elevation of critically endangered Bahama Orioles (Icterus northropi) to species status prompted us to evaluate their population status, habitat use, and breeding ecology. From surveys, we estimated that at least 141 to 254 individuals remain globally, with 90 to 162, 24 to 44, and 27 to 48 individuals remaining on North Andros Island, Mangrove Cay, and South Andros Island, The Bahamas, respectively. Orioles were observed nesting exclusively in anthropogenic habitat (residential and agricultural land), but home ranges also included nearby pine forest and coppice (dry broadleaf forest). Most nests (40 of 46, or 87%) were in nonnative coconut palm (Cocos nucifera), with native Sabal palmetto and Thrinax morrisii, and an introduced Brassaia actinophylla also used. Trees selected by orioles for nesting were significantly taller, less likely to have shrubs underneath, further from cover, and had more palm trees nearby than randomly selected palm trees. Three of eight nests with known contents were parasitized by Shiny Cowbirds (Molothrus bonariensis). Lethal yellowing disease recently devastated coconut palms and reduced the number of orioles on North Andros, but palms on Mangrove Cay and South Andros remain healthy. The juxtaposition of anthropogenic habitat to suitable native habitats may be more important than any single factor for Bahama Orioles, especially for breeding adults and fledged young. Conservation of coppice habitat, at high risk for agricultural and residential development, is crucial for survival of this critically endangered synanthropic species.

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Section: Discussionmentioning

confidence: 99%

Population status, habitat dependence, and reproductive ecology of Bahama Orioles: a critically endangered synanthropic species

Price¹,

Lee²,

Hayes³

2011

Journal of Field Ornithology

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“…Although conservation plans should focus on all available information, conservation resources spent on larger islands should affect more species, on average and with other things being equal. This rationale is fundamental and central to our analyses and conclusions, both here and in Trevino et al (2007) and Karels et al (2008).…”

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confidence: 92%

“…As we pointed out (Trevino et al 2007), a path coefficient of 1.0 should occur if the islands exhibited a constant proportion of threatened species. We have also performed a similar estimation for the null expectation of the number of extinct species on oceanic islands (since European colonization; Karels et al 2008), and found that the estimated path coefficient from size of the original avifauna to the number of species that had gone extinct ( p = 0.88) was much higher than the empirical value ( p = 0.36). Path coefficients lower than expected indicate heterogeneity among islands, such that both threats to current bird faunas and extinctions in the past influence some islands more than others (Karels et al 2008).…”

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confidence: 93%

“…First, the probability of threat of extinction is incorporated in our original path model as the relationship between the number of extant bird species on an island and the number of threatened bird species of the island. This is given a thorough explanation in Trevino et al (2007) and Karels et al (2008) and therefore will not be discussed further here. Second, the path coefficients in our analyses reflect the actual relationships that occur among the data variables, given their accuracy and consistency of measurement.…”

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confidence: 97%

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Importance of Causal Analysis of Threats to Oceanic Avifaunas: Reply to Blackburn et al.

Trevino¹,

Skibiel²,

Karels³

et al. 2008

Conservation Biology

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We are pleased that Blackburn et al. (2008 [this issue]) have taken an interest in our causal modeling of threatened bird faunas on oceanic islands (Trevino et al. 2007). Our results indicated possible environmental influences on the number of threatened bird species from the physical and biotic characteristics of islands. Blackburn et al. discuss possible strengths and weaknesses of 2 methods of analyzing such influences: generalizedlinear mixed modeling and causal modeling with structural equations and standardized partial-regression coefficients (these last used as measures of effect sizes). The former method excludes information because it does not incorporate the logical structure of causes, whereas the latter takes advantage of the fact that physical aspects of islands (island area and isolation from a mainland) might influence biotic factors (number of species in the avifauna, number of introduced mammalian predators, and time since human colonization of the islands) and that physical and biotic factors might influence the dependent variable (number of bird species under threat of extinction) (Fig. 1). Although physical factors are likely to influence biotic factors, we think the reverse is unlikely to be true. The method we used allowed us to test an a priori theoretical model that is a working hypothesis of causal mechanisms (Mitchell 1992) threatening birds on oceanic islands. This method can be used to refine and deepen understanding of the potential collaborative factors that may influence the extinction threat of ocean island avifaunas.Blackburn et al. estimated a null expectation for the number of threatened species from the size of the avifauna. As we pointed out in our original article, "the larger the avifauna on an island, the greater the number of bird species that can potentially become threatened with extinction" (Trevino et al. 2007:129). Blackburn et al. estimate the correlation for this relationship for random data §email trevihs@auburn.edu at about 0.74 and the regression weight at 0.60 (given random data), which is higher than the empirical correlation of 0.47 and regression weight 0.43. They insightfully point out that our path of 0.61 from number of extant avifauna to number of threatened avifauna is positive, as is the null hypothesis. Nevertheless, our path of 0.61 was a standardized, partial regression coefficient calculated after controlling for the effects of other variables and is not directly comparable to simple linear regression coefficients. These paths are interpreted as the proportional change in standard deviation of the dependent variable to a change of 1 SD in the independent (causal) variable (Li 1981). As we pointed out (Trevino et al. 2007), a path coefficient of 1.0 should occur if the islands exhibited a constant proportion of threatened species. We have also performed a similar estimation for the null expectation of the number of extinct species on oceanic islands (since European colonization; Karels et al. 2008), and found that the estimated path coefficient from ...

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“…Like Blackburn et al. (2004), Karels et al. (2008) also found both area and number of introduced mammalian predators to be important.…”

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confidence: 96%

Testing causal structure in the biogeography of avian extinctions on oceanic islands

Karels

Dobson

Zimbler-DeLorenzo

et al. 2009

Journal of Biogeography

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In their recent comment in this journal, T. M. Blackburn and colleagues called into question the use of standardized partial regression modelling (also called path analysis and structural equation modelling) when null expectations for regression coefficients are not zero. Here, we answer their critique by showing how randomization can be used to illuminate and interpret causal modelling in analyses that have non‐zero expectations. Causal modelling is a powerful tool that can yield novel insights in biogeography when properly interpreted.

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ORIGINAL ARTICLE: The biogeography of avian extinctions on oceanic islands

Cited by 22 publications

References 16 publications

Population status, habitat dependence, and reproductive ecology of Bahama Orioles: a critically endangered synanthropic species

Population status, habitat dependence, and reproductive ecology of Bahama Orioles: a critically endangered synanthropic species

Importance of Causal Analysis of Threats to Oceanic Avifaunas: Reply to Blackburn et al.

Testing causal structure in the biogeography of avian extinctions on oceanic islands

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