Habitat use and ecological interactions of an introduced and a native species of Anolis lizard on Grand Cayman, with a review of the outcomes of anole introductions
TL;DR: Review of data concerning 23 Anolis introductions indicates that the presence or absence of an ecologically similar native species may be an important determinant of colonization success or failure.
Abstract: Since its introduction ten years ago, Anolis sagrei has spread over much of Grand Cayman and is now more common in some habitats than the native anole, A. conspersus. Interspecific differences in body size, perch height, and microclimatic preference may have facilitated the colonization. Nonetheless, competition may be occurring between the species; comparisons with studies of habitat use prior to the arrival of A. sagrei indicate that in open habitats, where A. sagrei is now abundant, A. conspersus perches higher, but in closed habitats, where A. sagrei is absent, no change in perch height is evident. Review of data concerning 23 Anolis introductions indicates that the presence or absence of an ecologically similar native species may be an important determinant of colonization success or failure.
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TL;DR: Public attitudes about the need for conservation of reptiles are probably linked to concern about amphibian declines and deformities, and counts of “officially” recognized endangered and threatened species are likely to grossly underestimate the actual number of imperiled s pecies.
Abstract: A s a group [reptiles] are nei t h er ‘good ’n or ‘b ad ,’ but ia re intere s ting and unu su a l , a l t h o u gh of m i n or i m port a n ce . If t h ey should all disappe a r, it wo u l d not make mu ch differen ce one way or the other ”( Zim and Smith 1953, p. 9 ) . Fortu n a tely, this op i n i on from the Golden Gu i de Series does not persist tod ay; most people have com e to recogn i ze the va lue of both reptiles and amph i bians as an i n tegral part of n a tu ral eco s ys tems and as heralds of envi ron m ental qu a l i ty (Gibbons and Stangel 1999). In recent ye a rs , as overa ll envi ron m ental aw a reness among the p u blic has incre a s ed , con cerns have come to inclu de intere s t in the eco l ogical state of reptile and amph i bian spec i e s t h em s elves and of t h eir habi t a t s . In c re a s ed aw a reness may s tem from bet ter edu c a ti on abo ut threats to bi od ivers i ty in gen era l , and to reptiles and amph i bians in parti c u l a r, a n d po s s i bly even from an innate attracti on to these taxa ( Kell ert and Wi l s on 1993). From the perspective of many nonscientists, the two vertebrate classes comprising reptiles and amphibians, collectively referred to as the herpetofauna, are interchangeable. For example,the Boy Scout merit badge pamphlet for herpetology was called simply Reptile Study from 1926 to 1993 (Conant 1972, Gibbons 1993), and major zoos (e.g., National Zoo in Washington, DC; Zoo Atlanta; and San Diego Zoo) use only the name “reptile” to refer to the facility that houses both amphibians and reptiles. Thus, public attitudes about the need for conservation of reptiles are probably linked to concern about amphibian declines and deformities (Alford and Richards 1999, Johnson et al. 1999, Sessions et al. 1999), which have been the subject of numerous, well-documented scientific studies. Because amphibians are distributed worldwide, but herpetologists who document amphibian declines are not, it is difficult to accurately assess what portion of amphibian populations are experiencing significant declines or have already disappeared. Furthermore, the means of determining a species’ conservation status is a rigorous and time-intensive process, and therefore counts of “officially” recognized endangered and threatened species are likely to grossly underestimate the actual number of imperiled s pecies (Ta ble 1). The worl dwi de amph i bian decl i n e probl em , as it has come to be known, has garnered significant attention not only among scientists but also in the popular media and in political circles.
1,624 citations
TL;DR: It is shown that one key to invasion success may be the occurrence of multiple introductions that transform among- population variation in native ranges to within-population variation in introduced areas.
Abstract: A genetic paradox1,2 exists in invasion biology: how do introduced populations, whose genetic variation has probably been depleted by population bottlenecks, persist and adapt to new conditions? Lessons from conservation genetics show that reduced genetic variation due to genetic drift and founder effects limits the ability of a population to adapt, and small population size increases the risk of extinction1,3,4. Nonetheless, many introduced species experiencing these same conditions during initial introductions persist, expand their ranges, evolve rapidly and become invasive. To address this issue, we studied the brown anole, a worldwide invasive lizard. Genetic analyses indicate that at least eight introductions have occurred in Florida from across this lizard's native range, blending genetic variation from different geographic source populations and producing populations that contain substantially more, not less, genetic variation than native populations. Moreover, recently introduced brown anole populations around the world originate from Florida, and some have maintained these elevated levels of genetic variation. Here we show that one key to invasion success may be the occurrence of multiple introductions that transform among-population variation in native ranges to within-population variation in introduced areas. Furthermore, these genetically variable populations may be particularly potent sources for introductions elsewhere. The growing problem of invasive species introductions brings considerable economic and biological costs5,6. If these costs are to be mitigated, a greater understanding of the causes, progression and consequences of biological invasions is needed7.
1,014 citations
Cites background from "Habitat use and ecological interact..."
...sagrei is highly invasive; it reaches high population densities, shows exponential range expansion and is competitively superior to and a predator of native lizard...
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TL;DR: Character displacement research in the past two decades provides sound statistical support for the hypothesis in a wide variety of taxa, albeit with a phylogenetically skewed representation.
Abstract: Ecological character displacement, mostly seen as increased differences of size in sympatry between closely-related or similar species, is a focal hypothesis assuming that species too similar to one another could not coexist without diverging, owing to interspecific competition. Thus, ecological character displacement and community-wide character displacement (overdispersion in size of potential competitors within ecological guilds) were at the heart of the debate regarding the role of competition in structuring ecological communities. The debate has focused on the evidence presented in earlier studies and generated a new generation of rigorous, critical studies of communities. Character displacement research in the past two decades provides sound statistical support for the hypothesis in a wide variety of taxa, albeit with a phylogenetically skewed representation. A growing number of studies are strongly based in functional morphology, and some also demonstrate actual morphologically related resource partitioning. Phylogenetic models and experimental work have added to the scope and depth of earlier research, as have theoretical studies. However, many challenging ecological and evolutionary issues, regarding both selective forces (at the inter- and intraspecific level) and resultant patterns, remain to be addressed. Ecological character displacement and community-wide character displacement are here to stay as the focus of much exciting research.
523 citations
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TL;DR: Adult males in both the allopatric and sympatric conditions showed a significant and positive correlation between snout-vent lengths and the relative complexity and height of their immediate microhabitat, which suggests that there is intraspecific competition among males.
Abstract: Anolis cooki and Anolis cristatellus are sympatric lizards engaged in intense interspecific competition. We have identified and analyzed a critical area of competitive interference by measuring various niche dimensions and behavioral interactions under natural conditions. Four study areas of similar habitat composition were established within 5 km of each other: one allopatric for A. cooki, one allopatric for A. cristatellus and two sympatric areas. The variables of cloacal temperatures, perch height, perch diameter and habitat type were compared between lizards in and among the study areas. No significant differences in the variables were found between the sexes of a species or between species on the allopatric areas, nor were there differences between sympatric and allopatric A. cristatellus. Sympatric A. cooki males and females, however, exhibited a significant divergence from their allopatric counterparts by utilizing standing dead vegetation and small bushes rather than larger and more complex microhabitat. This shift was most likely in response to competitive interference from A. cristatellus. Except for sympatric A. cooki, adult males in both the allopatric and sympatric conditions showed a significant and positive correlation between snout-vent lengths and the relative complexity and height of their immediate microhabitat. This suggests that there is intraspecific competition among males, with the larger conspecific males controlling the taller and more complex habitat. Thus when the sympatric male A. cooki occupy small types of microhabitat, they are only likely to encounter the smaller size classes of A. cristatellus males. Intruder-release experiments showed that encounters between male A. cooki and A. cristatellus were very aggressive, similar in intensity to conspecific interactions. Less than one out of two times were resident A. cooki able to evict A.
41 citations
Journal Article•
41 citations
TL;DR: It is argued that much of the available evidence is either inconclusive, incorrect, or more consistent with the character-displacement model.
Abstract: revealed an interesting pattern: on most islands with only one species, that species is of intermediate size, but two-species islands usually contain both a large and a small species (Schoener, 1970; Table 1). The evolution of large and small size has often been interpreted as an example of character displacement (e.g., Schoener, 1988b; Williams 1972; Losos, 1990). Roughgarden and associates (e.g., Roughgarden et al., 1987; Roughgarden and Pacala, 1989; Rummel and Roughgarden 1985a) have proposed an alternative hypothesis; they argue that a taxon cycle is operating in the northern Lesser Antilles in which a larger species invades an island occupied by an intermediate-sized species, and both evolve smaller size until the former species is intermediate in size and the latter species is extinct (Fig. 1). Roughgarden and Pacala (1989) reviewed the pertinent data and concluded that the available evidence overwhelmingly favors the taxon-cycle model. Here I argue that much of this evidence is either inconclusive, incorrect, or more consistent with the character-displacement model.
37 citations
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