Vascular Plant and Vertebrate Inventory of Saguaro ... - USGS

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Estimating Abundance Estimating population size is a common goal of biologists who are motivated by the desire to reduce (pest species), increase (endangered species), maintain (game species) or monitor (indicator species) population size. Our surveys at the park were generally focused on detecting species rather than estimating population size. In many cases, however, we present estimates of “relative abundance” by species to provide information on areas in which species might be more or less common. Relative abundance is an index to population size; we calculate it as the number of individuals of a species recorded, scaled by survey effort. If we completed multiple surveys in comparable areas, we included a measure of precision (usually standard error) with the mean of those survey results. Indices of abundance are presumed to correlate with true population size but ecologists do not typically attempt to account for variation in detectability among different species or groups of species under different circumstances. Metrics (rather than indices) of abundance do consider variation in detection probability, and these include density (number of individuals per unit area; e.g., one Arizona black rattlesnake per km 2 ) and absolute abundance (population size; e.g., 30 Arizona black rattlesnakes at the district). These estimates are beyond the scope of our research. While it is true that indices to abundance have often been criticized (and with good reason, c.f. Anderson 2001a), the abundance information that we present in this report is used to characterize the commonness of different species rather than to quantify changes in abundance over long periods of time (e.g., monitoring). As such, relative abundance estimates are more useful than detectability-adjusted estimates of density for only a few species or raw count data for all species without scaling counts by survey effort. Sampling Design Overview Sampling design is the process of selecting sample units from a population or area of interest. 4 Unbiased random samples allow inference to the larger population from which those samples were drawn and enable one to estimate the true value of a parameter. The precision of these estimates, based on sample variance, increases with the number of samples taken; theoretically, random samples can be taken until all possible samples have been selected and precision is exact – a census has been taken and the true value is known. Non-random samples are less likely to be representative of the entire population, because the sample may (intentionally or not) be biased toward a particular characteristic, perhaps one of interest or convenience. In our surveys we employed both random and non-random spatial sampling designs for all taxa. For random sites, we colocated all taxonomic studies at the same sites (focal points and focal-point transects; see below for more information) because some characteristics, especially vegetation, could be used to explain differences in species richness or relative abundance among transects. We also used vegetation floristics and structure to group transects into community types that allowed more accurate data summaries. The location of nonrandom study sites was entirely at the discretion of each field crew (i.e., plants, birds, etc.) and we made no effort to co-locate them. Focal Points and Focal-point Transects: Random Sampling To account for differences in plant and animal communities at different elevation zones (e.g., Whittaker and Niering 1965) at the district, we used a stratified random design using elevation to delineate three strata: 6,000 feet. We chose a stratified design over a simple random design because stratified sampling better captures the inherent environmental variability within each stratum, allowing for greater precision of parameter estimates and increased sampling efficiency (Levy and Lemeshow 1999). This design also generates a better spatial dispersion of sampling units. Further, we chose to delineate strata based on elevation because it can be a good predictor of changes in vegetation and animal
communities and is especially useful when no reliable vegetation maps exist, as was the case for the district. Locating Random Study Sites We used the following process to assign the location of random study areas. First, we created 100 random (hereafter referred to as “focal”) points using the Animal Movement extension for ArcView (developed by the USGS Alaska Science Center – Biological Science Office), using uniform distribution, allowing zero meters to the district boundary, and zero meters between points. For each focal point, we generated a random bearing (the numbers ranged from 0 to 359). We then used the Bearing and Distance extension for ArcView (developed by Ying Ming Zhou, March 29, 2000; downloaded from ESRI ArcScripts website) to create points based on the distance and bearing from the original points. This gave us start points and end points for all 100 focal points. We then used the “from” and “to” coordinates to draw the transect line using A B C D E 100m 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 5 an Avenue script (“Draw line by coordinates,” developed by Rodrigo Nobrega, August 13, 1998; downloaded from ESRI ArcScripts website). The result was randomly placed, 1000-m line transects (hereafter referred to as “focal-point transects” or “transects”). Focal-point transects were not allowed to overlap. If this occurred, an entire new selection was conducted until a scenario of no overlapping transects was achieved. Many focal-point transects were not used because (1) some part of them lay outside of the district boundary, (2) at least 67% of the line did not fall within a single stratum, or (3) they were in areas where the terrain was too steep to work safely (i.e., crossed areas with slopes exceeding 35 degrees). These “danger” areas were derived from 30-m Digital Elevation Models using the Spatial Analyst extension for ArcView. The final design produced four bird-survey stations spaced 250 m apart; 10, 100 x 100 m amphibian and reptile plots; and 20, 50 x 50 m mammal plots along the focal-point transect line (Fig. 1.1). We sampled 1 2 3 3 4 4 Figure 1.1. Layout of 1-km focal-point transects showing layout of amphibian and reptile plots (C), small-mammal trapping grids (D), and bird survey stations (E).
Page 1: Powell, Halvorson, Schmidt Vascular
Page 4 and 5: U.S. Department of the Interior DIR
Page 7 and 8: Table of Contents Report Dedication
Page 9 and 10: Table 5.8. Number of breeding behav
Page 11 and 12: Figure 6.5. Locations of non-random
Page 13 and 14: Report Dedication Eric Wells Albrec
Page 15 and 16: Acknowledgements Thanks to Saguaro
Page 17 and 18: Executive Summary This report summa
Page 19 and 20: Chapter 1: Introduction to the Inve
Page 21: them out. This information, in conj
Page 25 and 26: Chapter 2: Park Overview Brian F. P
Page 27 and 28: Figure 2.2. Aerial photograph showi
Page 29 and 30: Figure 2.4. Diagram of the major ve
Page 31: Non-native Species and Changes to V
Page 34 and 35: General Botanizing Methods We colle
Page 36 and 37: Figure 3.3. Locations of modified-W
Page 38 and 39: Focal-points: General Patterns We f
Page 40 and 41: Percent 120 100 80 60 40 20 0 Plant
Page 42 and 43: well (Swantek et al. 1999). The mos
Page 45 and 46: Chapter 4: Amphibian and Reptile In
Page 47 and 48: Figure 4.2. Locations of intensive
Page 49 and 50: features. We based extensive survey
Page 51 and 52: B). Reptilian species included two
Page 53 and 54: Table 4.6. Relative abundance (mean
Page 55 and 56: Table 4.8. Relative abundance (mean
Page 57 and 58: Cumulative number of species 50 40
Page 59 and 60: elevation range of the district all
Page 61: in recent years due to sedimentatio
Page 64 and 65: Spatial Sampling Designs We establi
Page 66 and 67: Figure 5.2. Location of section bre
Page 68 and 69: the relative abundance by repeat-vi
Page 70 and 71: Analysis We report relative abundan
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with some pine trees, mostly pinyon
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Riparian Sonoran Desertscrub Oak Pi
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Table 5.5. Mean relative abundance
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Table 5.6. Relative abundance (mean
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Nest Adults carrying objects Other
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Cumulative number of species Cumula
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can impact other native plant and v
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Chapter 6: Mammal Inventory Don E.
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Figure 6.3. Locations of random (fo
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calculated relative abundance by pl
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Figure 6.5. Locations of non-random
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(2) Receiver triggers camera to tak
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Excluding the results for the white
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Table 6.5. Number of photographs of
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Cumulative number of species Cumula
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point out that the pond at Manning
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There is some suggestion that popul
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Chapter 7: Literature Cited Albrech
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Davis, R., and C. Dunford. 1987. An
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Kirkpatrick, C., C. J. Conway, and
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Rice, J., B. W. Anderson, and R. D.
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orderlands. Pp. 15-16. In effects o
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100 Family Scientific name Common n
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130 Order Voucher Specimen (S), Fam
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132 UA survey type Survey or specie
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138 Survey type Documentation type
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Voucher Collection type Taxon Speci
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Appendix F. List of existing vouche
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Taxon Common name Collectiona Colle
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Appendix G. Mean frequency of detec
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Species Total transects observed Lo
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Oak Savannah Pine-oak Woodland Coni
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Appendix I. Details of small-mammal
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Random or Camera Number of Number o
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