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: Five Cuban species of the neotropical iguanid genus Anolis were studied in the field to determine their body temperatures and habitat temperatures, and five of the species presented an opportunity to study thermal relations in tropical reptiles.
Abstract: The relation of a reptile's body temperature to that of the surrounding environment has been of considerable interest since the work of Cowles and Bogert (1944), and Bogert (1949a). These authors demonstrated that by behavioral methods reptiles were able to maintain their body temperature within a relatively narrow range. Reptiles, in other words, were shown to exhibit a degree of homeostasis in regard to their body temperature. The preferred or eccritic body temperature, was not the same for all the species studied. However, Bogert (op. cit.) demonstrated that lizards belonging to the same genus have similar body temperatures, while there may be marked differences between genera. Virtually all work reported for lizards has been with basking (heliothermic, Cowles, 1940) forms that gain heat from radiant energy. These heliothermic species raise their temperature above that of the surrounding air, and may achieve differences as great as 31 ? C between their body temperature and that of the surrounding air (Strelnikov, 1944; Pearson, 1954). With few exceptions (Inger, 1959; Bogert, 1949b) the species that have been studied are all temperate region forms, and actually the most intensively studied species have been from semiarid regions. In this investigation five Cuban species of the neotropical iguanid genus Anolis were studied in the field to determine their body temperatures and habitat temperatures. Two of the species were also studied in the laboratory to augment the findings in the field. The five species presented an opportunity to study thermal relations in tropical reptiles. As St. Girons and St. Girons (1956) emphasize, little is known about the thermal relations of tropical reptiles. The tropics represent the zone of the greatest abundance of species and individuals of reptiles. This abundance is in part attributable to the narrow temperature fluctuations of the lowand tropics where the temperature extremes of temperate and subtropical semiarid areas are never encountered. These five Cuban species represent an extraordinary example of habitat differentiation between closely related species in contiguous habitats. At the localities studied in central Cuba all five species are present, yet each is segregated in a specific ecological niche. As will be described below, the habitats range from the deep shaded portions of the forests, to the margins of the forests where filtered sunlight is present, to the open exposed habitats of the pastures and savannas.
193 citations
"Habitat use and ecological interact..." refers background in this paper
...sagrei are thermophilic and use low habitats (Collette 1961; Ruibal 1961; Salzburg 1984),just as A....
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TL;DR: Differences in head length and snout-vent length were computed for all combinations of Anolis species taken two at a time on the Greater Antilles to study the tendency to converge and diverge associated with structural-habitat similarity and spatial overlap.
Abstract: Differences in head length and snout-vent length were computed for all combinations of Anolis species taken two at a time on the Greater Antilles. There is a tendency to converge associated with structural-habitat similarity: Males of species whose range projections on a map do not overlap are significantly closer in size if structural habitats are similar than if different. There is a tendency to diverge associated with spatial overlap: Species with substantial structural habitat similarity are more different in head and snout-vent length if their ranges overlap than if allopatric. When a given species overlaps in part of its range with a second smaller species of similar structural habitat, convergence in head and snout-vent length is about as frequent as divergence; that is, the given species is as likely to increase its size as to decrease that size. Relatively large species converge significantly more often in this situation than do smaller species. However, where a given species overlaps in part of ...
186 citations
"Habitat use and ecological interact..." refers background in this paper
...In the Lesser Antilles, ecological coexistence is primarily a function of body size ( Schoener 1970; Roughgarden 1992)....
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TL;DR: A logical framework for an island-biogeographic theory based on species interactions and invasions and for the protection of fragile native species from invading exotics is provided.
Abstract: Islands or habitat patches in a metapopulation exist as multi-species communities. Community interactions link eachspecies' dynamics so that the colonization of one species may cause the extinction of another. In this way, communityinteractions may set limits to the invadability of an island and to the likelihood of resident species extinctions uponinvasion. To examine the nature of these limits, I assemble stable multi-species Lotka-Volterra competition communities thatdiffer in resident species number and the average strength (and variance) of species interactions. These are then invaded withspecies whose properties are drawn from the same distribution as the residents. The invader success rate and the extinctionrate of resident species is determined as a function of community- and species-level properties. I show that the probabilityof colonization success for an invader decreases with species number and the strength and variance of interspecificinteractions. Communities comprised of many strongly interacting species limit the invasion possibilities of competingspecies. Community interactions, even for a superior invading competitor, set up a sort of “activation barrier”that repels the invader. This “priority effect” for residents is not assumed a priori in mydescription for the individual population dynamics of these species, rather it arises because species-rich andstrongly-interacting species sets have alternative stable states that tend to disfavour species at low densities. These modelspoint to community-level rather than invader-level properties as the strongest determinant of differences in invasion success.If an invading species is successful it competitively displaces a greater number of resident species, on average, as communitysize increases. These results provide a logical framework for an island-biogeographic theory based on species interactions andinvasions and for the protection of fragile native species from invading exotics.
173 citations
TL;DR: Results imply that animals similar to widespread forms in some niche dimension other than structural habitat are those most likely to cause shift in structural habitat and suggest existence of a competition function with respect to size.
Abstract: This study analyzes the circumstances under which certain lizards shift and fail to shift their habitats. At each of 20 localities, I measured the structural habitats utilized by all the diurnal arboreal lizard species as well as the availability of those habitats. I selected localities so as to include for four widespread species (Anolis grahami, A. sagrei, A. carolinensis, A. distichus) nearly all of the species—combinations in which they occur. Data were fitted to equations that (1) adjust for locality—specific differences in vegetation, and (2) estimate the direction and intensity of apparent interaction between sympatric forms. Shift was valuated both for species and separately for age and sex classes within species. Female—sized individuals shift more frequently than do adult ♂ ♂. Linear equations that evaluate sympatric forms one at a time showed the strongest apparent competitors for a widespread from to be (1) adult ♂ ♂ rather than female—sized individuals, especially when adult ♂ ♂ represent the widespread species; (2) species of similar climatic habitat; (3) classes of similar size (especially against female—sized individuals of widespread species; and (4) classes of large size (especially against adult ♂ ♂). The most abundant classes are the strongest apparent competitors for A. distichus but not for the other widespread species. These results are unchanged or strengthened when different habitat categories or nonlinear equations are used. Combining all sympatric forms into locality—specific linear equations supports Results 1 and 2 but is inconclusive for Results 3 and 4. The parameter proportional to the size of a refugium from interference is estimated for some cases to be significantly greater for female—size individuals than for adult ♂ ♂. In general, results imply that animals similar to widespread forms in some niche dimension other than structural habitat are those most likely to cause shift in structural habitat. In addition, they suggest existence of a competition function with respect to size: in such a function intensity of competition is uniquely determined by the direction and amount of size difference, regardless of the competitors' absolute sizes. Competition intensity appears to (1) decrease overall with increasing difference in size, (2) be greater for a given size difference if the competitor is larger than if it is smaller, and (3) decrease at nonconstant rates, such that near complete size similarity there is a more rapid decline in intensity for smaller than larger competitors. Morphological differences between populations and short—term field observations suggest that both evolutionary and behavioral mechanisms regulate habitat shift.
169 citations
"Habitat use and ecological interact..." refers background in this paper
...ability, which may account for shifts in perch height (Schoener 1975)....
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TL;DR: Interspecific competition seems to have been an important process in determining extinction rate and, by extension, the equilibrium number of species on these islands.
Abstract: We discuss the patterns of introduction and extinction of the species of land birds (passeriforms and columbiforms) introduced to the Hawaiian Islands over the last century. The data are consistent with the idea that rising extinction rates will eventually match immigration rates leading to a dynamic equilibrium. Turnover in species composition is a prominent feature of the introduced Hawaiian avifauna with extinctions common even among populations that had persisted for decades. We could not detect an effect of island size on extinction rate. However, the per species extinction rates do increase with the number of species on the island. This suggests that the species mutually affect each other's chances of extinction. Other explanations for an increasing per-species extinction rate do not seem to be consistent with our data. Thus, interspecific competition seems to have been an important process in determining extinction rate and, by extension, the equilibrium number of species on these islands.
148 citations
"Habitat use and ecological interact..." refers background in this paper
...The study of introductions of non-native species can provide valuable data relevant to understanding the dynamics of community assembly (e.g., Moulton and Pimm 1983, 1986 )....
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