David J. Germano

Longevity and Age-Size Relationships of Populations of Desert Tortoises

Based on minimum estimates of longevity of desert tortoises (Gopherus agassizii) that died in the field, few individuals live past 50 yr. Approximately 29% of tortoises from the Sonoran Desert, 11% of tortoises from the eastern Mojave Desert, and approx. 5% of tortoises from the western Mojave Desert were estimated to be over 25 yr. The greatest estimate of longevity for any individual was 48-53 yr and came from the eastern Mojave Desert. The oldest individual from the western Mojave Desert was estimated to be 32 yr, and the oldest individual from the Sonoran Desert was estimated to be 35 yr. Comparisons of carapace length to age showed the highest rates of growth (0-25 yr) for tortoises from the western Mojave Desert and Sinaloan habitats. Of the four major regions within the range of the desert tortoise, rates of growth were lowest in the eastern Mojave and Sonoran deserts.

Shell Morphology of North American Tortoises

-Significant differences exist in adult carapace lengths among the four species of North American tortoises (Gopherus spp.). However, after measures of whole shell and scute dimensions are adjusted for these size differences, shape is more similar between the largest species, G. favomarginatus, and the smallest species, G. berlandieri, than with either of the intermediate-sized species, G. polyphemus and G. agassizii. Recent data based on an analysis of mitochondrial DNA of North American tortoises provide a phylogeny of the four extant species. A phenogram based on a multivariate analysis of 31 scute and shell measurements of North American tortoises is not concordant with a phenogram based on genetic data, although relationships among three major populations of G. agassizii are the same. Morphometric data are also not concordant with a matrix based on measures of precipitation and temperature, but are significantly correlated with a matrix based on growth variables (R2 = 0.74, P = 0.029). Other environmental parameters may affect shape of shells.

The San Joaquin Desert of California: Ecologically Misunderstood and Overlooked

ABSTRACT: The vegetation community of the San Joaquin Valley of California has been formally classified as a perennial grassland based largely on assumptions of past climax state. However, historical records suggest that the region might be more accurately classified as a desert. The distinction is important in determining the appropriate management strategies for this ecosystem, particularly for the many rare and endemic taxa that reside there. Abiotic and biotic factors—including low precipitation, arid soils, and desert-adapted plants and vertebrate—are consistent with conditions typical of desert areas. We examined the distributions of these factors to define the extent of the San Joaquin Desert. We conclude that the San Joaquin Desert historically encompassed 28,493 km2 including the western and southern two thirds of the San Joaquin Valley, and the Carrizo Plain and Cuyama Valley to the southwest. However, this ecosystem has been reduced by up to 59% from agricultural, industrial, and urban activities. The conservation of the unique biodiversity of this region is dependent upon this ecosystem being appropriately managed as a desert and not as a perennial or annual grassland.

Population Ecology of Blunt-Nosed Leopard Lizards in High Elevation Foothill Habitat

Abstract We captured 1078 Blunt-Nosed Leopard Lizards (Gambelia sila) 2396 times between 1989 and 1994 on the Elkhorn Plain, San Luis Obispo County, California. Based on size at first capture, we caught 119 adult (≥90 mm snout–vent length [SVL]) and 430 hatchling/juvenile (<90 mm SVL) males, and 139 adult and 390 hatchling/juvenile females. Sex ratio of males to females was 1.04 (549 males/529 females). Adult G. sila generally became active in April, and activity remained relatively high into July. Hatchlings were first noted in either July or August and generally could be found until early November, except in 1990 when no hatchlings were found at any time. Mean number of adults and hatchlings found active each day differed significantly across years, but as many as 32 adults and 42 hatchlings were seen on a plot during a census. Estimates of population abundance on a plot also varied yearly from 20–164 adults and 0–273 hatchling/juveniles and seemed to be affected either by too little or too much rain. Differences in daily activity varied and were moderately well explained by environmental factors. We estimated survivorship of lizards and found 29.0% of hatchlings from 1992 survived to 1993, and 14.6% of hatchlings from 1993 survived to 1994. The oldest G. sila found was a female estimated to be 4 years, 10 months when last caught, although most adults were not seen after 2 yr. Growth of individuals varied by year: highest growth rates were for lizards that hatched in 1991 and 1992, and lowest growth occurred in lizards that hatched in 1989. We found adult leopard lizards with eggs in all years but 1990. Females generally were gravid by late April or early May, and some females were found with eggs in early July. Female size at first reproduction was about 90 mm SVL, clutch size ranged from 1–6 eggs, and overall mean clutch size regardless of year or clutch order was 3.4 eggs. Many females produced multiple clutches in a year, and we found up to four clutches by a single female.

Differences in Habitat Use by Blanding’s Turtles, Emydoidea blandingii, and Painted Turtles, Chysemys picta, in the Nebraska Sandhills

Abstract We sampled a variety of wetlands in the Nebraska sandhills at Valentine National Wildlife Refuge. Significantly more individuals of painted turtles (Chrysemys picta) occurred in lakes and open waters than in marshes or small ponds, and the opposite was true for Blandings turtles (Emydoidea blandingii). Besides this marked difference in habitat use, 46% of the captured E. blandingii in pond/marsh habitat were juveniles, but only 31.6% in lakes and open water. Current information suggests that marshes and small ponds are important habitat for juvenile turtles, especially Emydoidea blandingii.

Variation in Body Size, Growth, and Population Structure of Actinemys marmorata from Lentic and Lotic Habitats in Southern Oregon

Abstract Turtle body size and growth rates are affected by several environmental factors, including thermal regimes. Small lentic habitats in northern latitudes often are thermally stratified in summer and, overall, provide a warmer environment than lotic habitats, which usually lack stratification because of flowing current. Several studies indicate that the amount of food consumption and rate of growth of turtles are higher, and body size larger, in warmer environments than cooler habitats. However, few sites have been examined. To better test these patterns, we compared the growth, body size, and population structure of the Western Pond Turtle (Actinemys marmorata) from six small lentic and four lotic habitats in southern Oregon. We found that adult size and growth rates were the same for the four lotic habitats and variable but not consistently greater at lentic sites. There were a high proportion of large turtles at all lotic sites but a variable proportion of sizes among lentic sites. Age structures did not match size structures for most populations because we found many young turtles in these populations but few small-sized turtles. Thus, we caution against reliance on size alone as a measure of population structure or trends in turtle populations. Further, our study suggests that sampling at a relatively large number of sites (e.g., ≥3 of each habitat type) improves inference of results.

Scutes and Age Determination of Desert Tortoises Revisited

Early investigators of desert tortoises, Gopherus agassizii (Miller, 1932, 1955; Woodbury and Hardy, 1948) dismissed as inaccurate the use of scute layers (rings) for determining age of individuals. However, many other investigators had demonstrated the annual deposition of scute layers used to determine the age of younger turtles (Sergeev, 1937; Cagle, 1946; Galbraith and Brooks, 1987; see full review in D. J. Germano and R. B. Bury, unpubl.), and scute layers were used to determine age in several tortoise species (e.g., Grubb, 1971; Castanet and Cheylan, 1979; Landers et al., 1982). In addition, Legler (1960) specifically showed that Woodbury and Hardy (1948) misunderstood how to apply the use of scute layers in desert tortoises. Given this controversy, I tested the use of scute layers to determine age of younger desert tortoises by counting the number of scute annuli of known-age tortoises at the Nevada Test Site in 1985. I found that the number of

Ecology of Western Pond Turtles (Actinemys marmorata) at Sewage-Treatment Facilities in the San Joaquin Valley, California

Abstract The western pond turtle (Actinemys marmorata) has lost most of its habitat in the Central Valley of California to agricultural activities, flood control, and urbanization. Although a few areas still support this turtle, most habitats are now altered by humans. Aquatic habitats near population centers also may become release sites for a variety of introduced turtles, which could compete with the native A. marmorata. In 1999, 2002, and 2007, I trapped at the Fresno and Hanford wastewater-treatment facilities to determine presence and numbers of A. marmorata at settling ponds in these facilities. I caught 213 A. marmorata at Fresno and 106 at Hanford. No other species of turtles was caught. Turtles at both sites grew rapidly and had a mean size of clutch of 8.2 (Fresno) and 8.5 eggs (Hanford), which are the highest mean size of clutch reported for this species. Although not esthetically appealing to people, both sewage-treatment facilities provide habitat for A. marmorata and these could provide stock for future reintroductions of this species to more natural, rehabilitated aquatic habitats in nearby areas.

Population Structure and Growth of the Turtle Actinemys marmorata from the Klamath-Siskiyou Ecoregion: Age, Not Size, Matters

Abstract Determining the demographic structure of turtles is important to understanding their population status and conservation needs. Concern has been raised for the long-term persistence of the Western Pond Turtle (Actinemys marmorata) based on demographic analyses using size while ignoring age. Here, we compare the size versus age structures, and examine growth curves, for turtle populations from four sites in the Klamath–Siskiyou ecoregion of northern California and southern Oregon. We show that age structure does not correspond to size structure for two populations. Also, the most abundant of these populations had relatively few small turtles, which suggests inability of previous researchers to locate small turtles. Growth rates and adult size differed among populations, with turtles from two sites in the Coast Range significantly smaller and slower growing than turtles from either a reservoir on the eastern lower slopes of the Coast Range or the Klamath Basin east of the Cascade Mountains. Neither air temperature nor elevation explained the differences in size and growth rates. We hypothesize that larger body size and faster growth rates for some populations of A. marmorata may be due to high local productivity. We show that use of size alone gave an erroneous interpretation of population structure. Finding a few small-sized turtles in populations may not represent a lack of recruitment but, instead, a need to determine the proportion of young turtles based on their actual ages.

Effect of Drought on Blunt-Nosed Leopard Lizards (Gambelia sila)

We studied a population of blunt-nosed leopard lizard (Gambelia sila) on the Elkhorn Plain, California from 1988-1991. Sufficient precipitation fell during the winters of 1987-1988 and 1990-1991 to produce abundant herbaceous ground cover the following springs. Winter rains in 1988-1989 produced low amounts of ground cover, and rains in 1989-1990 did not cause any appreciable number of annual plants to germinate. Counts of grasshoppers differed significantly between 1990 and 1991, with 10-60 times more grasshoppers counted in 1991 than 1990. In 1988, 1989, and 1991, adult leopard lizards, together with yearlings that hatched the preceding year, emerged from winter torpor in the spring and remained active through June. A few adults remained active into August, and in 1991 into September. In these same years, hatchlings appeared aboveground in August, and stayed active into September or October. However, in 1990, only yearling lizards were found active aboveground, and no reproduction occurred. Adult Gambelia sila have the ability to remain belowground > 21 mo during periods of low prey abundance. One of the density-independent factors of the environment that can affect populations of lizards is drought. Periods of below-average rainfall will decrease growth of plants, particularly herbaceous annuals, which in turn can depress populations of arthropods. Blunt-nosed leopard lizards (Gambelia sila) are mainly insectivorous (Montanucci 1965; Tollestrup 1979; Kato et al. 1987). Years with below-average precipitation can directly affect this species by lowering abundance of its prey. Gambelia sila is listed as an endangered species throughout its range in the San Joaquin Valley of California, and approximately 15% of its habitat remains (Germano and Williams 1993a). Understanding the response of populations of G. sila to environmental fluctuations is necessary for planning its recovery. In this paper, we discuss the ecology of a population of G. sila during a period of drought. We monitored changes in activity and reproduction of this species over four years, and correlated these changes with variation in environmental conditions. We discuss our results in light of possible responses that a long-lived lizard could make to a variable environment.