Allison C. Alberts

Occurrence Patterns of Bird Species in Habitat Fragments: Sampling, Extinction, and Nested Species Subsets

Comparison of the species-area relationship in unfragmented chaparral habitat with that in urban chaparral fragments confirmed that rapid population extinction of resident bird species has occurred in these fragments. A strong positive correlation between the relative persistence ability of a species and its density remains even after correcting for the sampling effect of area. We conclude that this pattern is due to differences between species in extinction vulnerability attributable to density; the more abundant species persist longer in fragments. This differential vulnerability to extinction produces a pattern in which the bird species present in species-poor fragments are nested subsets of those in species-rich fragments.

Constraints on the Design of Chemical Communication Systems in Terrestrial Vertebrates

Relations between structure, function, and constraint in the chemical communication systems of terrestrial vertebrates are examined from a design-feature perspective. A survey of chemical signals from 34 mammalian species indicates variation in the chemical structure of signals that are used in different social contexts and under different environmental conditions. Behavioral, physiological, and morphological adaptations in the emission and reception of chemical signals in terrestrial vertebrates are reviewed. Several features of chemical signals, including temporal parameters, spatial range, localizability, intensity and detectability, and information content, appear to be adjusted for particular social functions, subject to constraints of the signaling environment. In many cases, these adaptations may minimize energetic costs to signaling animals.

The effects of habitat fragmentation on chaparral plants and vertebrates

The effects of fragmentation in a scrub habitat in California on three taxa (plants, birds, and rodents) are concordant. Extinctions within the habitat remnants occur quickly and the sequence of species disappearances of birds and rodents is predictable based on population density in undisturbed habitat. Distance effects on species diversity are weak to non-existent, and habitat area effects are strong. Edge effects and cumulative habitat loss following isolation of the remnants are correlated with loss of species diversity. Recolonization in these taxa occurs rarely. Rodents appear to be extremely susceptible to extinction. Small, old patches retain a predictable subset of bird and rodent species, reinforcing the principle that larger reserves are generally superior

RESPONSE OF RODENTS TO HABITAT FRAGMENTATION IN COASTAL SOUTHERN CALIFORNIA

We employed an island biogeographic approach to determine whether small fragments of the shrub habitats coastal sage scrub and chaparral, isolated by urbanization, are capable of supporting viable populations of native rodent species. The distribution of native rodents in 25 urban habitat fragments was assessed by live-trapping. Over half of the fragments surveyed (13 of 25) did not support populations of native rodents. Fragments supported fewer species than equivalently sized plots in large expanses of unfragmented habitat, and older fragments (fragments that had been isolated for a longer period of time) supported fewer species. Both results implied that local extinctions occurred in the fragments following insularization. Stepwise multiple polychotomous logistic regression was used to determine which biogeographic variables were the best predictors of species number across fragments. The area of shrub habitat in each fragment was the most significant predictor of species diversity; age of a fragment was also significant and was negatively correlated with species number, but the isolation distance of a fragment had no relationship to species diversity. We found a negative relationship between extinction vulnerability of native rodent species and relative abundance: species that were more abundant in unfragmented habitat persisted in more habitat fragments. Random environmental and demographic fluctuations (island effects) and edge effects associated with fragmentation are proposed as causes of these local extinctions.

Chemical properties of femoral gland secretions in the desert iguana,Dipsosaurus dorsalis.

This study investigates the chemistry of femoral gland secretions in the desert iguana,Dipsosaurus dorsalis (Lacertilia: Iguanidae), and discusses their possible functional significance. Electrophoretic and proton NMR studies indicated that the secretions are composed of approximately 80 % protein and 20% lipid material. Individual differences in polyacrylamide gel banding patterns of femoral gland proteins were found. Reflectance spectroscopy revealed that the secretions strongly absorb longwave ultraviolet light, a feature that may be important in the localization of secretion deposits in the environment.

Seasonal productivity of lizard femoral glands: Relationship to social dominance and androgen levels

Social and hormonal correlates of femoral gland productivity were investigated in groups of adult and juvenile green iguanas (Iguana iguana) over 12 months. Femoral gland productivity, pore size, and the percentage of lipids in the secretions were correlated with plasma testosterone (T) levels in dominant, although not in subordinate, adult males. Secretory activity peaked during the breeding months, at which time dominants produced more secretion than subordinates. Pore size in juvenile males was positively correlated with plasma T levels and frequency of headbob displays in the months corresponding to the adult breeding season. After 18 months of age, individuals that performed visual displays had significantly larger pores than individuals that did not display. These results indicate that femoral gland secretions could function in the ontogeny and maintenance of dominance relationships.

Seasonal variation of lipids in femoral gland secretions of male green iguanas (Iguana iguana).

Femoral gland secretions were collected from 21 captive adult male green iguanas (Iguana iguana) in Orotina, Costa Rica, and San Diego, California, during the breeding (November) and nonbreeding (March) seasons. Lipids were extracted with methylene chloride, weighed, separated by thin-layer chromatography, and analyzed by gas chromatography-mass spectrometry. Free and esterified C14-C26 fatty acids, 5β-cholestan-3α-ol (epico-prostanol), cholest-5-en-3β-ol (cholesterol), cholest-5-en-24-methyl-3β-ol (campesterol), cholesta-5,22-dien-24b-ethyl-3β-ol (stigmasterol), cholesta-8,24(5α)-dien-4,4,14α-trimethyl-3β-ol (lanosterol), cholest-5-en-24-ethyl-3β-ol (β-sitosterol), and two uncharacterized sterols were indicated. More lipids were recovered from femoral gland secretions obtained during the breeding than the nonbreeding months, indicating that secretion deposits may be more detectable during the mating season.

Effects of Incubation Temperature and Water Potential on Growth and Thermoregulatory Behavior of Hatchling Cuban Rock Iguanas (Cyclura nubila)

To examine the effects of incubation temperature and moisture levels on embryonic development and posthatching growth and behavior, we incubated a total of 123 eggs collected from 18 wild female Cuban rock iguanas at 28.0, 29.5, or 31.0 C on wet (-150 kPa), moist (-550 kPa), or dry (-1100 kPa) substrates. Although there was no effect of incubation temperature or water availability on egg survival, larger females exhibited higher infertility and greater mortality of initially viable eggs, suggesting that reproductive senescence may occur in this long-lived species. Incubation temperature, although it had little influence on size at hatching, significantly affected several measures of growth, including changes in body length, mass, and head dimensions. In general, hatchlings from higher incubation temperatures grew faster during their first year. However, by 16 months of age, growth rates no longer varied among hatchlings incubated at different temperatures. Incubation temperature had no detectable effect on thermal selection by hatchlings at 14 to 16 months of age, as there was no tendency for hatchlings incubated at higher temperatures to preferentially select higher basking temperatures. Moisture levels during incubation did not significantly affect size, growth, or thermoregulatory behavior of hatchlings. These results have important implications for understanding how environmental conditions experienced during embryonic development may affect future fitness

Sources of intraspecific variability in the protein composition of lizard femoral gland secretions

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Differential resource use, growth, and the ontogeny of social relationships in the green iguana

Growth rates, resource use, and ontogeny of behavior patterns were examined in captive groups of juvenile green iguanas (Iguana iguana). Four groups were housed in large arenas where supplemental heat and perch sites were limited, whereas two control groups were housed in similar arenas without limited resources. Growth, frequency and types of displays, behavioral interactions, and the use of resources were monitored. By 35-70 days of age, male hatchlings in arenas with limited resources could be classified into two groups: rapid growing dominant individuals and slow growing subordinate individuals. Growth and dominance were not correlated with size of individuals at hatching. Digestive efficiency of males was related to dominance and access to limited resources, but all lizards exhibited a similar digestive efficiency when maintained at a constant ambient temperature. Dominant males used the resources, especially supplemental heat sources, twice as often as subordinate males. The dominant/subordinate relationships and accompanying skew in body size were not evident in the control groups, or in females of any group. At 105 days, control groups were introduced to conditions with limited resources, resulting in increased aggressive interactions and divergence in growth rates. Onset of adult behavioral patterns was related to body size, and the species-specific signature display was observed in dominant males up to several months before subordinate males. These results indicate that male green iguanas establish a dominance hierarchy immediately posthatching when resources are limited, and as a consequence, both physiological and behavioral maturation are delayed in subordinate individuals.