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Geology topics

Robert N. Fisher

Publications and source records attributed to Robert N. Fisher.

At least 235 records · Page 13Linked to original sources
USGS2004

Snake (Colubridae: Thamnophis) predatory responses to chemical cues from native and introduced prey species

Several aquatic vertebrates have been introduced into freshwater systems in California over the past 100 years. Some populations of the two-striped garter snake (Thamnophis hammondii) have lived in sympatry with these species since their introduction; other populations have never encountered them. To assess the possible adaptation to a novel prey, we tested the predatory responses of T. hammondii from different populations to different chemosensory cues from native and introduced prey species. We presented chemical extracts from potential prey types and 2 control odors to individual snakes on cotton swabs and recorded the number of tongue flicks and attacks directed at each swab. Subject response was higher for prey odors than control substances. Odors from introduced centrarchid fish (Lepomis) elicited higher response levels than other prey types, including native anuran larvae (Pseudacris regilla). The pattern of response was similar for both populations of snakes (experienced and nai??ve, with respect to the introduced prey). We suggest that the generalist aquatic lifestyle of T. hammondii has allowed it to take advantage of increasing populations of introduced prey. Decisions on the management strategies for some of these introduced prey species should include consideration of how T. hammondii populations might respond in areas of sympatry.

Southwestern Naturalist↗
USGS2004

Designing monitoring programs in an adaptive management context for regional multiple species conservation plans

Increasing numbers of regional, multiple species conservation plans have been developed in California since the early 1990s. However, building effective monitoring and adaptive management programs to support these plans has remained a challenge. In addition to collecting data on the status of resources and the results of management actions, monitoring programs for these plans need to resolve critical uncertainties and channel information into effective decisionmaking. Because of the broad goals of many regional conservation plans, monitoring programs need to address ecosystem integrity and biodiversity while also tracking species ?covered? by plan permits. In this document we provide a step-by-step procedure for developing effective monitoring programs in an adaptive management context. The guidance provided here has been gleaned from experience with large multiple species plans in southern California. The process begins with clearly defining program objectives, partitioning the program into manageable but meaningful pieces, and developing management-oriented conceptual models of system function. Then, based on the objectives and conceptual models, monitoring recommendations and critical uncertainties can be identified and a coordinated program designed. We include practical examples and insights from programs in southern California and discuss the evolution of monitoring and adaptive management programs through three successive stages: 1) inventorying resources and identifying relationships; 2) pilot testing of long-term monitoring and resolving critical management uncertainties; and 3) implementing long-term monitoring and adaptive management. Ultimately, the success of regional conservation planning depends on the ability of monitoring programs to confront the challenges of adaptively managing and monitoring complex ecosystems and diverse arrays of sensitive species.

Technical Report↗
USGS2003

Factors influencing the variation in capture rates of shrews in southern California, USA

We examined the temporal variation in capture rates of shrews Notiosorex crawfordi (Coues, 1877) and Sorex ornatus (Merriam, 1895) in 20 sites representing fragmented and continuous habitats in southern California, USA. In N. crawfordi , the temporal variation was significantly correlated with the mean capture rates. Of the 6 landscape variables analyzed (size of the landscape, size of the sample area, altitude, edge, longitude and latitude), sample area was positively correlated with variation in capture rates of N. crawfordi . In S. ornatus , longitude was negatively correlated with variation in capture rates. Analysis of the effect of precipitation on the short- and long-term capture rates at 2 of the sites showed no correlation between rainfall and capture rates of shrews even though peak number of shrews at both sites were reached during the year of highest amount of rainfall. A key problem confounding capture rates of shrews in southern California is the low overall abundance of both shrew species in all habitats and seasons.

California↗
USGS2001

Effect of land cover, habitat fragmentation and ant colonies on the distribution and abundance of shrews in southern California

Because effects of habitat fragmentation and anthropogenic disturbance on native animals have been relatively little studied in arid areas and in insectivores, we investigated the roles of different land covers, habitat fragmentation and ant colonies on the distribution and abundance of shrews, Notiosorex crawfordi and Sorex ornatus , in southern California. Notiosorex crawfordi was the numerically dominant species (trap-success rate 0·52) occurring in 21 of the 22 study sites in 85% of the 286 pitfall arrays used in this study. Sorex ornatus was captured in 14 of the sites, in 52% of the arrays with a total trap-success rate of 0·2. Neither of the species was found in one of the sites. The population dynamics of the two shrew species were relatively synchronous during the 4–5-year study; the peak densities usually occurred during the spring. Precipitation had a significant positive effect, and maximum temperature a significant negative effect on the trap-success rate of S. ornatus . Occurrence and abundance of shrews varied significantly between sites and years but the size of the landscape or the study site had no effect on the abundance of shrews. The amount of urban edge had no significant effect on the captures of shrews but increased edge allows invasion of the Argentine ants, which had a highly significant negative impact on the abundance of N. crawfordi . At the trap array level, the percentage of coastal sage scrub flora had a significant positive, and the percentage of other flora had a significant negative effect on the abundance of N. crawfordi . The mean canopy height and the abundance of N. crawfordi had a significant positive effect on the occurrence of S. ornatus . Our study suggests that the loss of native coastal sage scrub flora and increasing presence of Argentine ant colonies may significantly effect the distribution and abundance of N. crawfordi . The very low overall population densities of both shrew species in most study sites make both species susceptible to extinction in isolated habitat fragments due to environmental stochasticity, and anthropogenic disturbance.

Journal of Animal Ecology↗
USGS2001

Coastal sage scrub case study

In ecological applications of large-scale spatial data to management decisions concerning land planning and conservation, errors and biases may creep into the analysis and decision making at several steps (see Chaps. 1, 2, and 3), including: • Uncertainty in positions of spatial locations of relevant ecological and physiographic features of the landscape. • Uncertainty of the type and attributes of land cover at a particular location. • Uncertainty in how different land covers at a position in space and the geometric arrangement of land covers nearby might influence an animal species occurrence or distribution, or the magnitude of some ecological process. • Uncertainty about the relative importance of each spatial location to the overall success or persistence of a population or ecological process. • Uncertainty about how to weight each species or ecological process in determining the overall biodiversity and functioning of ecosystems, local and national resource priorities, and consistency with legislative mandates. We would like to be able to quantify the errors at each step, identify biases, and pass these along to the next analysis step so that our degree of uncertainty regarding potential outcomes is evident at each level (e.g., Stoms et al. 1992).

Book chapter↗
USGS2001

Pneumocystosis in wild small mammals from California

Cyst forms of the opportunistic fungal parasite Pneumocystis carinii were found in the lungs of 34% of the desert shrew, Notiosorex crawfordi ( n = 59), 13% of the ornate shrew, Sorex ornatus ( n = 55), 6% of the dusky-footed wood rat, Neotoma fuscipes ( n = 16), 2.5% of the California meadow vole, Microtus californicus ( n = 40), and 50% of the California pocket mouse, Chaetodipus californicus ( n = 2) caught from southern California between February 1998 and February 2000. Cysts were not found in any of the harvest mouse, Reithrodontomys megalotis ( n = 21), California mouse, Peromyscus californicus ( n = 20), brush mouse, Peromyscus boylii ( n = 7) or deer mouse, Peromyscus maniculatus ( n = 4) examined. All infections were mild; extrapulmonary infections were not observed. Other lung parasites detected were Hepatozoon sp./spp. from M. californicus and Notiosorex crawfordi , Chrysosporium sp. (Emmonsia) from M. californicus , and a nematode from S. ornatus .

California↗
USGS2001

Prey: Thamnophis hammondii (Two-striped Garter Snake)

Pox infection has occurrcd in mourning doves in at least 8 states on 12 separate occasions. Unsuccessful attempts were made to transmit both fowl pox (chicken isolate) and passerine pox (cowbird isolate) to mourning doves.

Herpetological Review↗