How To Find Raw Animal Population Data

8 Field Techniques for Population Sampling and Estimation

Field techniques refer to the standardized methods employed to select, count, mensurate, capture, mark, and observe individuals sampled from the target population for the purpose of collecting data required to attain study objectives. The term also includes methods used to collect voucher specimens, tissue samples, and habitat data. The option of field techniques to utilise for a detail species or population is influenced by five major factors:

1. Data needed to achieve inventory and monitoring objectives
2. Spatial extent and duration of the projection
3. Life history and population characteristics
4. Terrain and vegetation in the study area
5. Budget constraints

Data Requirements

The types of data required to accomplish inventory or monitoring objectives should be the primary consideration in selecting field techniques. Four categories of data collection are discussed beneath along with some suggestions for electing advisable field techniques for each.

Occurrence and distribution data

For some population studies, simply determining whether a species is nowadays in an area is sufficient for conducting the planned data assay. For example, biologists attempting to conserve a threatened salamander may need to monitor the extent of the species' range and degree of population fragmentation on a land ownership. One hypothetical approach is to map all streams in which the salamander is known to be present, as well equally additional streams that may qualify as the habitat blazon for the species in the region. To monitor changes in salamander distribution, information collection could consist of a survey forth randomly selected reaches in each of the streams to make up one's mind if at to the lowest degree ane private (or some alternative feature such equally egg mass) is present. Using only a listing that includes the stream reach (i.e., the unique identifier), the survey year, and an occupancy indicator variable, a biologist could set up a fourth dimension serial of maps displaying all of the streams by twelvemonth and distinguish the subset of streams that were known to be occupied by the salamander. Such an approach could back up a qualitative assessment of changes in the species distribution design, thereby attaining the program' objectives, and generate new hypotheses equally to the cause of the observed changes.

Information technology is far easier to make up one's mind if in that location is at to the lowest degree one individual of the target species on a sampling unit than it is to count all of the individuals. Determining with confidence that a species is not present on a sampling unit also requires more intensive sampling than collecting count or frequency information because it is so hard to dismiss the possibility that an individual eluded detection. Probability of occurrence can be estimated using approaches such as those described by MacKenzie and Royale (2005). MacKenzie (2005) offered an excellent overview for managers of the merchandise-off betwixt number of units sampled per yr and the number of years (or other unit of fourth dimension) for which the study is to be conducted. The variation in the estimated trend in occupancy decreases as the number of years of data collection increases (Fig. 8.1). A similar level of precision can be achieved by surveying more than units over fewer years vs. surveying fewer units over a longer menstruum.

Figure 8.one. Simulation-based coefficient of variation for estimated trend in occupancy (on the logistic calibration) where 50, 100, or 200 landscapes are each surveyed 3 times per flavor, for multiple seasons (redrafted from MacKenzie 2005). Estimates of occupancy can be facilitated by apply of computer programs such as PRESENCE (MacKenzie et al. 2003).

Population size and density

National policy on threatened and endangered species is ultimately directed toward efforts to increment or maintain the total number of individuals of the species within their natural geographic range (Suckling and Taylor 2006). Full population size and effective population size (i.e., the number of breeding individuals in a population; Lande and Barrowclough 1987) virtually direct betoken the degree of species endangerment and effectiveness of conservation policies and practices. Population size or more than accurately density per unit of measurement area is normally used equally the basis for trend analyses because changes in density integrate changes in natural mortality, exploitation, and habitat quality. In some circumstances, it may be viable to conduct a census of all individuals of a item species in an area to determine the population density. Typically nevertheless, population size and density parameters are estimated using statistical analyses based on only a sample of population members. Population densities of plants and sessile animals can exist estimated from counts taken on plots or information describing the spacing between individuals (i.east. distance methods) and are relatively straightforward. Population analyses for many creature species must account for animal response to capture or observation, observer biases, and unlike detection probabilities amid sub-populations. Pilot studies are usually required to collect the data necessary to address these factors in the analysis. Furthermore, mark-recapture studies, catch-per-unit of measurement effort surveys, and other estimation methods require multiple visits to sampling units (Pradel 1996). These considerations increase the complication and cost of studies designed for population parameter interpretation.

Abundance indices

The goals and objectives of some biological inventories and monitoring studies can be met with indices of population density or abundance, rather than population estimators. The difference between estimators and indices is that the former yield absolute values of population density while the latter provide relative measures of density that tin be used to compare indices to populations amidst places or times. Indices are founded on the assumption that index values are closely associated with values of a population parameter, although the precise human relationship between the index and parameter usually is not quantified. Examples of abundance or density indices are: plant awning embrace, numbers of individuals captured per g trap nights, counts of individuals observed during a standardized unit of fourth dimension, among many others. From a data collection perspective, density indices often require less sampling intensity and complication than population estimation procedures. However, population indices are not comparable amid different studies unless field techniques are strictly standardized. Furthermore, the assumption that an abundance alphabetize closely approximates population density is rarely tested (Seber 1982).

Fitness data

For rare or failing populations, estimates of survival in each life stage as well as reproductive rates are required. These data not only provide useful trigger points for estimating rates of turn down (lambda) they too permit trigger points for removal of a species from a threatened or other legal status. Collecting these sorts of data is oft labor intensive and expensive. In a report on northern spotted owls, for case, millions of dollars have been spent collecting these types of data (Lint 2001). This is not peculiarly surprising every bit the types of information that would exist necessary to understand the population dynamics of a bird are numerous and complicated to generate. Nest densities, clutch sizes, hatching rates, fledging rates, and survival rates to maturity and survival rates as reproductive adults would be a minimum data ready. New approaches to estimating individual contributions to population growth and changes in distributions of quantitative traits and alleles include genetic analyses, which can atomic number 82 to even more than detailed understanding of the potential for a population to adjust to variations in environmental factors (Pelletier et al. 2009).

Research studies

Studies of habitat relationships or cause-and-effect responses crave coordinated sampling of the target population and environmental measurements or stressors to which the population may respond. Data collection efforts tend to be complex, requiring multiple sampling protocols for the target population, study site attributes, and mural blueprint metrics. The funding required to behave research studies typically limits their awarding to species or populations in greatest need of management planning such as those listed as threatened or endangered. Manipulative studies are oft carried out to generate the necessary data, but when these focus on a threatened species, upstanding questions regarding the comport of the experiment placing the species at even great risk, at to the lowest degree locally, oft emerge. Hence it is often monitoring of both environmental conditions and aspects of population density or fitness that are used to assess associations in trends between population parameters and ecology parameters.

Spatial Extent

Conspicuously the scope of inference will influence the type of sampling technique used. Convenance bird atlas techniques usually use large grids placed over entire states to assess the occurrence of species in a grid cell. Such approaches and those of the Breeding Bird Survey (Sauer et al. 2008) can be conducted through volunteer efforts. On the other hand, monitoring the trends in reproductive rates of northern spotted owls, northern goshawks, or grizzly bears over their geographic ranges requires a huge budget to collect the level of population data over large areas needed to understand trends. Great care must be taken when deciding what technique to employ because both budgets and sample size requirements enter into logistics. Indeed, information technology is frequently the tradeoff between more detailed data and the cost of producing those data that drive decisions regarding monitoring designs for species at risk.

Frequently Used Techniques for Sampling Animals

The array of techniques bachelor to sample animals is vast and summarized elsewhere in techniques manuals (e.g., Bookhout 1994). We summarize a few examples of commonly used techniques, but strongly suggest that those of you developing monitoring plans practice a more than complete literature search on sampling of the species that are of most concern in your monitoring plan. Nosotros first provide a cursory overview of techniques used to sample vertebrates and and so point out which techniques are ordinarily used among various taxonomic groups.

Aquatic Organisms

Some aquatic organisms tin and take been monitored using techniques that are essentially identical to those used for terrestrial vertebrates. For case, in Brazil, arapaima have been monitored using a point count technique that counts individuals every bit they surface for aeriform animate (Castello et al. 2009). Point counts were more logistically and economically feasible, were adamant to more than accurately represent population changes over time and led to more effective management, but a conventional mark-recapture technique was too attempted with the same fish species (Castello et al. 2009).

Yet cases such as the arapaima are uncommon because this species is detected when surfacing for aerial breathing, has a low enough population density in a small plenty expanse to be counted effectively, and possesses certain subtle visual and acoustic characteristics that permit for the identification of individuals (Castello et al. 2009). Most techniques used to sample aquatic organisms are conceptually similar to those used to sample terrestrial organisms. But constraints placed on observers of dealing with sampling in or on the water and at various water depths require that many techniques be more specialized. There are a variety of techniques commonly used to sample fish and aquatic amphibians as well every bit aquatic invertebrates (Slack et al. 1973). A systematic assessment of stream reaches using either snorkel surveys (Hankin and Reeves 1988) or electrofishing equipment is ordinarily used in shallow streams and rivers (Cunjak et al. 1988).

In estuaries and large rivers, quantitative studies are oftentimes confounded by the high variability of fish populations and the high efficiency of fish sampling gear (Poizat and Baran 1997). In light of this, Poizat and Baran (1997) undertook a study assessing the efficacy of surveying fishermen compared with a scientist-managed gill-net sampling arroyo and adamant that combining both approaches is the best way to increment conviction that observed trends are real. In other words, if both sets of survey information advise the same trend, it is safer to infer that the trends are real than if the data sets advise different trends or at that place exists just i type of data.

Manta tows, which are comparable to line-transect methods only must business relationship for uniquely marine conditions such every bit turbidity of water, tides, and sea-condition characteristics, are often utilized to monitor full general characteristics of coral reefs and their associated populations. The technique, which has been employed in both scientist-run and community based programs, consists of towing a snorkeler trained to find sure variables backside a boat at abiding speed forth a pre-determined stretch of reef (Bass and Miller 1996, Uychiaoco et al. 2005). In one report forth the Swell Barrier Reef, where manta tows take been employed since the 1970s, the sampled line is broken up into zones that have ii minutes to sample and every two minutes, the gunkhole stops for the observer to record data on an aquatic data sheet (Bass and Miller 1996). In these surveys, data often include counts of conspicuous species, such as giant clams, or of entire assemblages, such as carnivorous and herbivorous fish, but the technique is also used for monitoring habitat (Bass and Miller 1996, Uychiaoco et al. 2005). Indeed, observations of suites of variables designed to inform practitioners almost the country of coral reefs over time such every bit reef slope, dominant benthic form, dominant hard coral genus, and structural complexity of coral are also usually recorded (Bass and Miller 1996, Uychiaoco et al 2005).

Welsh et al. (1987) proposed a habitat-based approach for amphibians in small headwater streams and fourth dimension-constrained and expanse-constrained approaches have also been used for headwater species (Hossack et al. 2006). Pond-breeding species or species that inhabit deeper water are often sampled using minnow traps, nets, or call counts of vocalizing frogs and toads (Kolozsvary and Swihart 1999, Crouch and Paton 2002).

Tracking of private animals through tags, passive integrated transponders (PIT tags) and similar techniques are expensive just provide information on animal movements and estimates of population size and survival. Such approaches have been used with species of high interest such as coho salmon in the Pacific Northwest (Wigington et al. 2006).

Terrestrial and Semi-Aquatic Organisms

The diversity of forms, sizes, and life histories amidst terrestrial vertebrates has led to the development of hundreds of field techniques designed for different species and survey atmospheric condition. Table 8.i lists the most widely used field techniques for collecting wildlife data, only it is past no ways an exhaustive listing of all inventory and monitoring methods. Techniques are separated into observational, capture, and marking methods and by the manner by which data are collected. A comprehensive review of all the unlike field techniques for terrestrial and semi-aquatic organisms is a separate book in itself (see Bookhout 1994). Hither we provide a brief overview of some of the commonly used techniques.

                           Kuenzi and Morrison 1998      TagsBirds/MammalsNietfeld et al. 1994

Table 8.1. Field techniques for inventories and monitoring studies of terrestrial and semi-aquatic vertebrates. References can be found in the Literature Cited section.

	Mode	Technique	Target Groups of Species	References
Observational	Directly	Quadrats; stock-still-surface area plots	Sessile or relatively immobile organisms	Bonham 1989
		Avian betoken counts	Bird species that sing or phone call on territories	Ralph et al. 1995
		Spot mapping & nest searches	Territorial bird species	Ralph et al. 1993
		Line transect	Large mammals, birds	Anderson et al. 1979
		Call playback response	Wolves, footing squirrels, raptors, woodpeckers	Ogutu and Dublin 1998
		Standardized visual searches	Large herbivores,	Cook and Jacobsen 1979
		Census	Cave-dwelling bats; large herbivores	Thomas and West 1989
	Animal Sign	Human foot track surveys	Medium-large mammals	Wilson and Delahay 2001
	Pellet & scat counts	Medium-large mammals	Fuller 1991
		Food cache searches	Large carnivores	Easter-Pilcher 1990
		Structures (e.g., dens, nests)	Arboreal mammals; fossorial mammals; bears	Healy and Welsh 1992
	Remote Sensing	Track plates	Medium-large mammals	Wilson and Delahay 2001
	Photo & video stations	Medium-large mammals	Morruzzi et al. 2002
		Ultrasonic detectors	Bats	Thomas and West 1989
		Audio monitoring	Frogs	Hunker and Paton 2002
		Hair traps	Minor-medium mammals, big carnivores	McDaniel et al. 2000
		Radio telemetry	Limited by animal body size (>xx g) ?	USGS 1997
		GPS telemetry	Limited by beast trunk ( >2000 g) ?	Girard et al. 2002
		Marine radar	Bats, migrating birds	Harmata et al. 1999
		Harmonic radar	Bats, amphibians, reptiles	Pellet et al. 2006
Capture	Passive	Pitfalls	Salamanders, lizards, small mammals	Enge 2001, Mengak and Guynn 1987
		Snap traps	Small mammals	Mengak and Guynn 1987
		Box traps	Small-medium mammals	Powell and Proulx 2003
		Funnel-type traps	Snakes, turtles	Enge 2001
		Leg-hold & snares	Large mammals	Bookhout 1994
		Mist nets
	Active	Drives to an enclosure	Medium-big mammals with predictable flight response	deCalesta and Witmer 1990
		Cannon nets	Medium-large mammals	Bookhout 1994
		Immobilizing agents	Big mammals	Bookhout 1994
		Manus capture	Salamanders	Kolozsvary and Swihart. 1999
Marker
		Mutilation	Pocket-sized mammals	Wood and Slade 1990
		Pigments	Small mammals	Lemen and Freeman 1985
		Collars & Bands	Birds/mammals	Nietfeld et al. 1994

For sure species and weather, it may exist feasible to determine a count of individual members of the population on quadrats (sample plots) randomly or systematically positioned in the study area. Searches can be conducted on foot, all-terrain vehicles, or airplane depending on the calibration and circumstances of the survey. Quadrat sampling is commonly used for plants and habitat elements, simply with animals quadrat sampling poses some challenges. If animals are mobile during the sampling period, then at that place needs to exist some reasonable assurance that an individual is not double-counted at multiple quadrats every bit information technology moves. Size, spacing, and mobility of the organisms must all be considered.

Point counts are peradventure the most extensively used technique for measuring bird abundance and diversity in temperate forests and on rangelands but have also been used to approximate abundance of other diurnal species such equally squirrels. Variations in the technique accept been described for different species and to meet different data needs (Verner and Ritter 1985, Verner 1988, Ralph et al. 1995, Huff et al. 2000). Ralph et al. (1995) provided a drove of papers examining sample size adequacy, bird detectability, observer bias, and comparisons amid techniques.

Spot mapping, also referred to every bit territory mapping, often is used to approximate avian population densities by locating singing males during a number of visits to the study area and delineating territory boundaries. The technique is further described in Ralph et al. (1995). Nest searches tin can be used to assess reproductive success in an avian population by monitoring the survival of eggs and nestlings over the course of a breeding season. Both techniques are labor intensive and are not usually used for inventories, only the information gained from these methods (i.east., territory densities, productivity) may be better indicators of population trends and habitat quality than only counts of individuals.

Line transect and point transect sampling are specialized plot methods in which a search for the target organism is conducted along a narrow strip having a known area. Rarely tin it exist causeless that all animals are detected forth the transect. However, if the probability of detection can be predicted from the distance betwixt the beast and the centerline of the transect, then a detection part can be used to estimate population density. The arroyo tin be adapted to surveys conducted past foot, snorkeling, and ground or air vehicles. Buckland et al. (1993) provided a complete, though highly technical, introduction to line transect and point transect methods. The arroyo has been widely applied to surveys of vertebrates, including desert tortoise (Anderson et al. 2001), marbled murrelets (Madsen et al. 1999), songbirds in oak-pine woodlands (Verner and Ritter 1985), and mule deer (White et al. 1989).

Audio recordings of creature vocalizations take been used to elicit calls and displays from species otherwise difficult to detect. The technique has been applied in studies of bluish grouse (Stirling and Bendell 1966), northern spotted owls (Forsman 1988), footing squirrels (Lishak 1977), and others. The number of responses past the target species elicited by the recording is tallied during a prescribed interval and provides a population density index.

Standardized visual searches refer to techniques used to decide species occurrence, species richness, or relative density values, where sampling effort is standardized by space or time. Examples include road counts for large mammals (Rudran et al. 1996), raptor migration counts (Hussell 1981), and visual come across surveys for terrestrial amphibians (Crump and Scott 1994) (Figure 8.two). Some visual search techniques do not necessarily equalize the corporeality of survey effort among sampling units. Instead, beast counts or species detected are standardized during analysis by dividing the number of observations by a unit of surface area or fourth dimension. Variability amid observers and environmental conditions may exist pregnant sources of error unassociated with the sampling technique and should exist assessed prior to data collection to minimize biases and improve precision.

Effigy 8.2. Ensatina salamander detected on a time constrained sample in managed forests of the Oregon Cascades. Prototype available via The Marion County Parks section.

Nether certain circumstances, it may be possible to finer observe all individuals in the target population. In such cases, population size can be determined directly from the count of individuals; no statistical procedures are necessary. Accurate counts on individuals depend upon a natural tendency of population members to amass, at least during anticipated periods (e.g., cave-roosting bats). Furthermore, all locations where the individuals aggregate must be known in the study area, and in that location must be acceptable surveyors available to make simultaneous counts at all locations.

In many cases, the target population is highly cryptic or besides wary to be observed directly and upkeep constraints foreclose the investigator from utilizing capture methods for information collection. In these situations, it is oft possible to infer the presence of a species or determine an index value for population density past observing animal signs. Signs are tracks, scat piles, fecal pellets, olfactory property-mark posts, or animal constructions (e.g., arboreal nests, beaver lodges, couch openings) that can exist accurately identified as prove of a particular species. If searches for such evidence are conducted on standardized transects or quadrats, and so observations may provide a reliable index to population density. Data analyses are like to that for direct observations. Davis and Winstead (1980) and Wemmer et. al (1996) provide an overview of methods based on animal sign.

Elusive species tin be sampled using remote sensing devices positioned beyond the study area. Track plates (Zelinski and Stauffer 1996) and hair traps (Scotts and Craig 1988, McDaniel et al. 2000) are inexpensive and suitable for determining the occurrence and distribution of rare mammals in the study area. Ultrasonic detectors tin can be used to monitor bat populations (Kunz et al. 1996), withal information technology is not always possible to reliably distinguish among all bat species. Remote camera stations with data-loggers (Cutler and Swann 1999, Moruzzi et al. 2002) non only detect occurrence of the species, but as well may yield data about sex, historic period, and activity patterns of individuals. Baits at a track plate or photographic camera station can be used to increase the probability on detecting a cryptic or rare species, merely tin can likewise bias whatsoever estimates fabricated or disproportionately concenter common omnivorous species, such equally Virginia opossum or northern raccoon (Figure 8.iii).

Figure eight.3. Virginia opossum attracted to a hair snare baited with apples. Baiting tin concenter animals and may increase the likelihood of detecting a species just may also give a biased index to abundance.

Radio-telemetry has been used for many years to collect data on wildlife and fish move, home range size, and habitat selection (Figure 8.4). Transmitters weighing <one.0 one thousand are now commercial available making it possible to track all just the smallest vertebrates. Tracking systems utilizing global positioning system (GPS) satellites let monitoring of animate being locations in real-fourth dimension without requiring surveyors to determine radio signal directions in the field and are condign more reasonably priced. A drove of abstracts on wildlife telemetry methods (USGS 1997) provides a useful introduction to the topic for terrestrial studies. Marine band radar has been used to count migratory birds at observation points (Harmata et al. 1999) and monitor activity patterns of marbled murrelets (Burger 2001).

Figure eight.4. Cheetah with a radio collar at Moremi Biological reserve, Botswana. Photograph by Nancy McGarigal and used with her permission.

Finally genetic analyses of tissue nerveless from hair traps, scat or other tissues take led to an explosion of approaches to appraise populations, dispersal, and evolutionary patterns (Haig 1998, Mills et al. 2000).

Life History and Population Characteristics

Certain techniques are more commonly used with some taxonomic groups than others. In this section we provide guidance as to the types of techniques that you lot might consider depending on the species included in your monitoring program.

Amphibians and Reptiles

The small size, cryptic nature, and fossorial habits of salamanders make data drove particularly difficult. Many terrestrial amphibians motility only brusk distances and are not susceptible to passive capture techniques. These species are commonly sampled using visual searches and hand capture techniques with sampling endeavour standardized past area (Jaeger and Inger 1994, Bailey et al. 2004) or a fourth dimension constraint (Crump and Scott 1994) (Effigy viii.two). Species that drift betwixt aquatic breeding ponds and terrestrial habitat types may be susceptible to pitfall traps with drift fences (Corn 1994). For pond-convenance species, egg masses are ofttimes more detectable than adults of the same species, making egg masses more suitable for population monitoring studies. Shaffer et al. (1994) and Olson et al. (1997) provided an splendid introduction to techniques for amphibian inventories in ponds.

Embrace-board surveys take been widely adopted for estimating the relative abundance of amphibian and reptile populations in different habitat types (Grant et al. 1992, Harpole and Haas 1999, Engelstoft and Ovaskake 2000). Cover-boards are objects such equally boards or metal covering that provides daytime encompass for animals and when lifted reveals a sample of the animals in the surface area that employ it (Figure 8.5). Hence it is a sample of a plot for those species that seek encompass.

Effigy 8.5. A gopher serpent and a garter snake uncovered from under a comprehend board used to sample reptiles in an Oregon oak savannah, Oregon.

Birds

As a grouping, many species of birds are sampled using altitude sampling because they are and so mobile and vocal (Rostenstock et al. 2002, and see Buckland et al. 1993 for an overview of distance sampling). Consequently there are two primary means of detecting many species of birds, increasing the likelihood that they may be detected, particularly during the breeding season when males are oftentimes territorial. Diurnal species sampled in grasslands, marshes or other rather uniform vegetation conditions often can be sampled using transects (e.g., Ribic and Sample 2001). Samples taken in areas where rugged terrain or other factors forbid the use of transects rely on indicate counts (Buckland 1987). Other commonly used techniques include spot mapping to empathize territory densities (e.g., Dobkin and Rich 1998), nest searches to understand nest densities, and variations on the Mayfield method of calculating nest success (Johnson and Shaeffer 1990). Nocturnal species nowadays additional challenges, but point counts for owls during their mating flavor can be effective especially if telephone call back recordings are used to elicit responses (Hardy and Morrison 2000). Merely call up recordings can introduce biases when recordings are played in areas having unlike vegetative structure or topography. Finally, banding and band returns can be used to guess longevity and historic period structures of populations (Pollock and Raveling 1982).

Mammals

Small mammals are often sampled using traps of various forms (Effigy viii.6). Live traps are often used equally they are suitable for marker-recapture estimates of population size, or live or kill traps tin be used to judge grab per unit effort estimates of relative affluence. When any kind of trap is used, beast welfare guidelines should be reviewed and followed.

Figure 8.six. Live traps fastened to trees are peculiarly effective at sampling flying squirrels and other arboreal species. Photo of flight squirrel past Cheron Ferland, used with permission. Photo of woman checking trap by Laura Navarrette and used with permission.

Detection probabilities are influenced past the number of trap-nights (the number of traps multiplied by the number of nights sampled). Capture rates are easily influenced by factors such every bit density-dependent intra-specific interactions, weather, and habitat, so capture probabilities must exist calculated to permit an unbiased estimate of relative abundance (Menkens and Anderson 1988). This is peculiarly of import when assessing trends over time during circumstances where weather and other conditions affecting catchability vary from yr to year.

Larger mammals, peculiarly those that form social aggregations or occur as amassed populations may exist more than finer surveyed by observational techniques than capture methods. Aerial surveys for ungulates are oft conducted using altitude sampling procedures, but once again observability among vegetation types, weather conditions, and topographies need to be considered to ensure unbiased estimates of abundance (Pollock and Kendall 1987).

Occurrence and indices to affluence for mid-size mammals are often addressed using remotely activated cameras, scent stations, rail counts or runway plates, or spotlight surveys (Figure viii.3; Gese 2001). Each of these techniques has advantages of being reasonably low cost and effective at detecting sure species (see Gese 2001), simply estimation of population size is usually not possible.

Bats present a unique sampling trouble. Using ultrasonic recordings of their feeding calls can help in distinguishing some species occurring in an surface area (O'Farrell et al. 1999), but estimates of affluence are often conducted at roost or maternity sites.

Furnishings of Terrain and Vegetation

Imagine that you are counting all the birds that you can see or hear forth a transect that extends from the eye of a forested patch to the center of an next field. You wish to decide if the relative affluence of birds differs between the 2 habitat types. Y'all detect 28 birds in the forest and 34 in the field. Are there more birds in the field than in the forest? Maybe. But probably not. Your power to detect birds in the woods is hampered by the decreased visibility in the woods compared to a more open field. Hence if you lot corrected for the differences in detectability as a function of the vegetation type (using techniques common in distance sampling) then the number of birds detected per unit expanse might be much greater in the forest than in the field. Consequently only raw counts of animals without considering the distance from the observer to the animal are frequently biased and should not be used as response variables in monitoring programs. This is particularly of import where vegetation structure is likely to change over the course of the monitoring time frame.

On man fourth dimension-scales, terrain does not (usually) change appreciably from one time period to another, but observations must still be standardized by their detectability in various settings.

Merits and Limitations of Indices Compared to Estimators

Indices are often used to assess changes in populations over fourth dimension based on an assumption that some aspect of detection is related to actual animal density. For case, the following are a few examples of indices to affluence:

• track counts (Conner et al. 1983)
• pellet grouping counts (Fuller 1991)
• capture rates (Cole et al. 2000)
• detection rates of singing male birds (McGarigal and McComb 1998)
• relative dominance (plant populations)
• counts of squirrel leafage nests (Healy and Welsh 1992)
• counts of beaver lodges or caches (Easter-Pilcher 1990)

These examples do not provide estimates of populations, rather, an index is measured with the assumption that the index is related to the population or its fettle in a known mode and that observed changes in the alphabetize measurement over time will reverberate changes in population co-ordinate to this relationship. Assumptions such equally the more tracks seen, the more individuals present; or the more male birds heard singing, the more birds reproducing at the site are often made. Only the reliability of these assumptions is brought into question, and indeed the opportunity for bias associated with indices to affluence is quite high. For instance, track counts may be related to animal abundance or to animal activity levels, but on the other hand, they could be related to the characteristics of the substrate, the weather, or whatever combination of these options. Too, counts of singing male birds may stand for trends in abundance of territorial males, just if some males do not attract a mate, then numbers of singing males may non indicate abundance of nesting females nor reproductive output. Capture rates of animals over infinite and fourth dimension tin can be related to animal abundance or to their vulnerability to capture in different areas of habitat quality. Consequently, although indices to abundance are oftentimes used because of logistical constraints, considerable circumspection must be exercised when interpreting the results. Indeed, it is frequently useful to conduct a airplane pilot study that will allow you to state with a known level of certainty what the relationship is betwixt the alphabetize and the actual population (or fettle) for the species being monitored. To do so requires an approximate of the population.

Estimators provide additional information to the user and can aid to address some of the biases inherent in many indices. Fortunately in that location are a number of tools bachelor to judge abundances that are based on sampling theory and can result in known levels of conviction placed effectually the estimates. For instance, distance estimators provide a mechanism for estimating abundance of organisms from points or transects where detectability might differ amid vegetative types or stream reaches. Population estimators are more often than not bachelor as gratuitous software: https://www.usgs.gov/software/wild fauna-software-and-models

A variety of data is used equally the footing for estimates of populations (capture-recapture and band returns), some of which can likewise provide estimates of survival and reproduction. The overwhelming advantage of using population estimators is that estimates of abundance, survival, and age grade distribution can be made with estimates of confidence. Clearly with replicate sampling of independent sites, indices to abundance tin can exist calculated with confidence intervals, but there is still doubt regarding the assumption of unbiased clan between the alphabetize and the population characteristic of interest. Consequently it is important when designing monitoring protocols to ensure that estimators are considered, and if it is not logistically possible to use estimators as a response variable in the monitoring program, then the selected alphabetize should be justified relative to its known association with the population characteristic of involvement. If this cannot be done, then both the assumptions and the implications of violating those assumptions should exist clearly stated.

Estimating Community Structure

Although much of this book focuses on monitoring species and the environmental weather in which they live, at times managers may exist concerned with maintaining or developing conditions that promote diverse or functional communities, or exist able to detect declines in functional diversity in the face of environmental stressors. Multifariousness metrics have evolved over decades and provide a ways of comparing complication between or among places or times. Unfortunately near diversity metrics also bury information on individual species responses within one or a few numbers. To sympathise what is really happening within a community, a diverseness metrics must be deconstructed to come across changes in private species or populations. The devil is indeed in the item. However diversity metrics are still used as a guide to community structure and function. Typically, a variety metric consists of an estimate of the number of species in a unit of infinite and fourth dimension (species richness) and the distribution of individuals among those species (evenness). In most evenness metrics, the maximum is achievable value is 1.00 (an equal number of individuals per unit area represented among all species in the customs; i.e., no species dominates the community). But consider the example in tabular array 8.2. The hypothetical wood and grassland have the same diversity and evenness. So are they the same community? Do they function in a like manner? Obviously not. In fact the degree to which the two communities are similar in species representation and distribution of individuals amid species in common between the two communities indicates that the percent similarity betwixt the two communities is 0. In fact, each customs has more than in common with a more species rich and more than even customs represented in a savannah than in the woods or grassland. So is the savannah improve because information technology is more than species rich and more diverse? No, it is just dissimilar. In short, these metrics of community construction can be very difficult to interpret without excavation into the details that comprise the metrics.

Table eight.ii. Example of estimates of species diversity and community similarity for three hypothetical communities.

	Community
	Forest	Savannah	Grassland
Black-capped chickadee	10	4	0
Song Sparrow	two	four	0
American robin	4	3	0
Grasshopper sparrow	0	three	4
Marsh wren	0	1	2
Savannah Sparrow	0	1	10
	___	___	___
Species Richness	3	6	3
Number of individuals	xvi	sixteen	xvi
Simpson'south Evenness	0.797	0.956	0.797
Simpson'due south Species Multifariousness1	0.567	0.850	0.567
Community similarity (%)2
Woods-Savannah	0.563
Forest-Grassland	0.000
Savannah-Grassland	0.313
1 White (1986)
2 Itow (1991)

Sampling communities in a fashion that produces unbiased estimates of community structure as well can be problematic. Species richness assessments may exist every bit simple equally developing a listing of species detected in an surface area using standardized techniques. But some species are probable more than easily detected than others. Some are active at different times of the 24-hour interval, and some move more others. Then estimates of richness are confounded past differences in detectability. When multifariousness metrics are calculated using these data, boosted complications ascend because estimates of abundance for each species in the community must be unbiased and based on the aforementioned unit of space and time. Again, differential detectability of species and biases resulting from movement ascend making evenness estimates confounded between bodily differences in abundance among species and differences in detection amid species. Surveys to determine the presence of a species in an area typically crave less sampling intensity than fieldwork necessary to collect other population statistics.

Another metric that can be calculated from data collected within a monitoring framework deals with diff sampling efforts when trying to estimate the number of species in an surface area. Because rare species are often less likely to exist detected than mutual species, one can estimate the number of species based on rarefaction curves so that you can compare the number of species institute in ii areas when the sampling try differed (Simberloff 1972).

Estimating biotic integrity

Karr (1981) adult and index to biotic integrity (IBI) that was designed to be used to compare aspects of fish communities amid sites in a standardized manner that reflected the h2o quality of the site with regards to its capacity to support fish communities. Information technology included aspects of species richness, fish health, and a number of other parameters. Researchers have since adjusted this technique for other taxa including aquatic macroinvertebrates and birds (Bryce et al. 2002). Although the general structure of IBIs is similar to that developed by Karr (1981), each IBI is typically crafted to a reference condition typical of the ecoregion within which a sampled area occurs. Hence an IBI adult for the mixed mesophytic forest of the Appalachians may have a similar structure to that of one in the Cascades mountains of Oregon, simply the parameters measured would be based on a very different fix of reference conditions. For that reason IBIs are not typically used in terrestrial monitoring protocols and like diversity indices they can coffin information that must be extracted past deconstructing the index.

Standardization Protocol Review

Regardless of the approach taken, certain aspects of a sampling design should be standardized to minimize bias in the resulting information. See chapter 7 for a more detailed overview of standardization techniques. At the very least specific attending should be paid to consistently sampling the aforementioned location over time, sampling during the same season and time of day and using the same equipment from one sampling menstruum to the next.

In addition to consistency in sampling techniques, locations and times, most of the approaches described in this chapter will need approval by an Institutional Animal Care and Use Commission (IACUC) or comparable review board at universities and agencies. Standards of Intendance for animals when conducting research are rigorous and should be applied to monitoring programs also (see Laber et al. 2007 and Hafner 2007 for a perspective on limitations to such reviews).

Budget Constraints

The choice of which sampling technique to utilize when presented with options and a gear up of goals and objectives is equally oft driven my constraints of time and money every bit by the platonic technique to acquire the data needed. For case, while information on survival of juveniles in the face up of climate alter may be a principal consideration for a long-lived species, a suitable surrogate might be an index to abundance of young of the yr and developed animals in the population. Since upkeep decisions are often fabricated based on the social seriousness of the consequence, and since social values change over time, so do budgets. Consequently it often is wise to develop a monitoring program using techniques that are robust to concerns regarding bias and precision and that are cost effective, fifty-fifty if they do non event in the platonic level of fitness data that would be needed to answer demographic questions more definitively. More detailed demographic information may be collected in a supplementary manner if the level of social concern reaches a indicate where it is mandated.

Summary

There is a huge array of methods available to notice, enumerate or assess the fettle of organisms. Matching the appropriate approach with the goals and objectives of the study is a key first pace in designing a monitoring program. The data needed to accomplish inventory and monitoring objectives is frequently the driving gene in deciding which techniques will exist used in a monitoring program. In improver the scale of the monitoring program may also influence the methods used. For narrowly focused programs on highly valued species, detailed measurements of fitness may exist advisable. Every bit the scale of the project over space and time increases, then estimates of abundance or occurrence may exist the most feasible approach.

Furthermore, different taxa vary in their propensity to be sampled using dissimilar methods. Whereas sessile animals tin can be sampled using quadrat sampling, wide-ranging species may more easily exist sampled using cameras or hair traps that may provide data on occurrence or individual movements. In a like way, just the logistics associated with sampling in inhospitable (to humans) terrain limits the choices of sampling strategies bachelor. Finally, budgetary and logistic restrictions oftentimes hateful that the platonic sampling system may not be feasible because the time or money is not bachelor to implement the technique to adequately run into the goals and objectives.

Amongst all of the decisions regarding which technique to utilize, yous should continually be aware of the demand to standardize approaches over space and fourth dimension and seek to minimize whatsoever biases in your sampling methods.

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