Comparison of Dietary Overlap between Allopatric and Sympatric Geckos

Klawinski, Paul D.; Vaughan, R. Kathryn; Saenz, Daniel; Godwin, William

doi:10.2307/1564624

Cited by 17 publications

(11 citation statements)

References 16 publications

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“…However, today several other, more recently introduced, gekkonid species compete with H. turcicus in some regions. For instance, at Port Galveston, Texas, H. turcicus has apparently been replaced by the recently introduced lizard Cyrtopodion scabrum (Klawinski et al. , 1994).…”

Section: Discussionmentioning

confidence: 99%

Niche shift versus niche conservatism? Climatic characteristics of the native and invasive ranges of the Mediterranean house gecko (Hemidactylus turcicus)

Rödder

Lötters

2009

Global Ecology and Biogeography

183

195

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Aim The use of ecological niche models (ENMs) to predict potential distributions of species is steadily increasing. A necessary assumption is that climatic niches are conservative, but recent findings of niche shifts during biological invasion indicate that this assumption is not always valid. Selection of predictor variables may be one reason for the observed shifts. In this paper we assess differences in climatic niches in the native and invaded ranges of the Mediterranean house gecko (Hemidactylus turcicus) in terms of commonly applied climate variables in ENMs. We analyse which variables are more conserved versus relaxed (i.e. subject to niche shift). Furthermore, we study the predictive power of different sets of climate variables. Location The Mediterranean region and North America.Methods We developed models using Maxent and various subsets of variables out of 19 bioclimatic layers including: (1) two subsets comprising almost all variables excluding only highly collinear ones; (2) two subsets with minimalistic variable sets of water availability and energy measures; (3) two subsets focused on temperature-related parameters; (4) two subsets with precipitation-related parameters; and (5) one subset comprising variables combining temperature and precipitation characteristics. Occurrence data from the native Mediterranean range were used to predict the potential introduced range in North America and vice versa. Degrees of niche similarity and conservatism were assessed using both Schoener's index and Hellinger distances. The significance of the results was tested using null models. ResultsThe degree of niche similarity and conservatism varied greatly among the predictors and variable sets applied. Shifts observed in some variables could be attributed to active habitat selection while others apparently reflected background effects. Main conclusionsThe study was based on comprehensive occurrence data from all regions where Hemidactylus turcicus is present in Europe and North America, providing a robust foundation. Our results clearly indicate that the degree of conservatism of niches in H. turcicus largely varies among predictors and variable sets applied. Therefore, the extent of niche conservatism of variables applied should always be tested in ENMs. This has an important impact on studies of biological invasion, impacts of climate change and niche evolution.

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Section: Discussionmentioning

confidence: 99%

Niche shift versus niche conservatism? Climatic characteristics of the native and invasive ranges of the Mediterranean house gecko (Hemidactylus turcicus)

Rödder

Lötters

2009

Global Ecology and Biogeography

183

195

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“…(2) finding natural situations where both competitors exist in isolation from one another; or (3) by increasing resource availability so that competition is removed (Klawinski et al 1994). Investigating the second option was a possibility, but the invertebrate fauna and habitat structure were markedly different on Ile aux Aigrettes compared to islands where the two geckos existed in isolation from one another (Cole 2005).…”

Section: Discussionmentioning

confidence: 99%

Environmentally-induced shifts in behavior intensify indirect competition by an invasive gecko in Mauritius

Cole

2011

Biol Invasions

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Most recorded extinctions have occurred on oceanic islands, mainly as a result of introduced mammalian predators. The impact of introduced nonmammalian competitors, however, is poorly understood. The house gecko, Hemidactylus frenatus, is one of the most successful invasive reptiles and has been implicated in the decline of endemic geckos and other taxa on a number of tropical and subtropical islands. We investigated the patterns of niche utilization between the house gecko and endemic ornate day gecko, Phelsuma ornata, in Mauritius, two species which were not believed to compete because they had different diel activity periods. The dietary and temporal niche partitioning of the two species were examined in relation to seasonal invertebrate prey abundance for three seasons. Dietary overlap between the two species was least when prey abundance was lowest and temporal overlap in activity greatest. Exploitative competition was therefore inferred, whereby changes in dietary overlap were attributed to shifts in prey selection by the day, but not the house, gecko, which was hypothesized to deplete prey. The compensatory response of the day gecko may have been to increase its tendency for cannibalism, such that the smaller house gecko was indirectly responsible for population reduction of its larger competitor. This is the first study to show how an invasive nocturnal gecko may be affecting a predominantly diurnal species.

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“…However, several studies did not report prey volume data in a way I could re‐analyse, perhaps because prey volume is often considered less important than number of prey items (Magnusson et al 2003) or because some lizard species finely chew and fragment prey prior to swallowing, thus impeding reliable measurements of volume (Klawinski et al 1994). In some instances (Mesquita et al 2006), original sources reported a dietary importance index, or an average value between prey item number and prey volume, but did not report actual numbers or volume.…”

Section: Methodsmentioning

confidence: 99%

Do lizard communities partition the trophic niche? A worldwide meta‐analysis using null models

Luiselli¹

2007

Oikos

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Lizards have been widely used as model organisms in community ecology over the past 30 years. I have reviewed more than 50 studies from the literature on the community ecology of lizards worldwide, with a focus on studies from 1990Á 2007. I determined if there is support for the hypotheses that many lizard communities 1) are non-randomly organized along the trophic niche dimension, and 2) partition the available food resource to minimize interspecific competition. I used data on number of prey items and percentage of prey volume, to calculate dietary overlap among species. I compared true datasets to randomly generate new datasets produced by 3 )10 4 Monte Carlo permutations using two algorithms (RA2 and RA3). The great majority (more than 80%) of the communities were randomly organized along the trophic niche dimension using RA2 or RA3; the frequency of occurrence of detecting a non-random structure in lizard community dietary studies did not differ significantly between datasets based on either number of prey items or prey volume. Thus, lizard communities usually do not partition the trophic niche axis. Concerning the number of prey items, logistic regression models showed that the presence of a structure in the dataset did not depend on number of species, method employed to obtain dietary data, matrix size, or location (continent), but instead significantly depended on whether a community was tropical. Concerning prey volume, presence of a structure in the dataset also did not depend on number of species, method employed to obtain dietary data, and tropical vs non-tropical origin, but was marginally dependent on continent (South America was favoured for identifying a structure in the dataset) and matrix size. In general, a structure in the dataset was more often uncovered by using RA2 than RA3. Overall, I conclude that 1) lizard communities are unlikely to partition available food resources, and 2) as the method for identifying dietary items does not allow for accurate prey identification (at least at the genus level), there is a risk of obtaining false null results about community structure. This is because structure along the trophic niche axis is genuinely rare in lizards and also because inappropriate methods may erroneously lead to this conclusion. Therefore, conclusions from studies utilizing stomach dissection as a source of diet data (still common in the literature) should be cautiously considered for ethical reasons and because it is difficult to find any difference between stomach-dissection and fecal-pellet data when assessing the presence of a structure in datasets. My data also showed there are minor differences in the probability of detecting a structure in datasets using prey item number or prey volume data for lizards. The biases, both statistical and biological, associated with this meta-analysis are discussed.

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Comparison of Dietary Overlap between Allopatric and Sympatric Geckos

Abstract: ABSTRAC~.-Two gecko species, Hemidactylus turcicus and Cyrtopodion scabrum, have been introduced into the Port of Galveston, Texas. While H. turcicus has been established for a longer period of time, the-relatively recent introduction of C.

Cited by 17 publications

References 16 publications

Niche shift versus niche conservatism? Climatic characteristics of the native and invasive ranges of the Mediterranean house gecko (Hemidactylus turcicus)

Niche shift versus niche conservatism? Climatic characteristics of the native and invasive ranges of the Mediterranean house gecko (Hemidactylus turcicus)

Environmentally-induced shifts in behavior intensify indirect competition by an invasive gecko in Mauritius

Do lizard communities partition the trophic niche? A worldwide meta‐analysis using null models

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