Abundance Of Animal Populations Research Articles

Point transect sampling with traps or lures

SummaryThe ability to monitor abundance of animal populations is becoming increasingly important, in light of growing concerns over the loss of biodiversity through anthropogenic changes. A widely used tool for such monitoring is distance sampling, in which distances of detected animals from a line or point are modelled, to estimate detectability and hence abundance. Nevertheless, many species still prove problematic to survey. We have developed two extensions to point transect sampling that potentially allow abundance to be estimated for a number of species from diverse taxa for which good survey methods have not previously been available.For each method, the primary survey comprises a random sample of points, or more usually a systematic grid of points, through the region of interest. Animals are lured to a point, or trapped at a point, and the number of animals observed at each point is recorded. A separate study is conducted on a subset of animals, to record whether they respond to the lure or enter the trap, for a range of known distances from the point. These data are used to estimate the probability that an animal will respond to the lure or enter the trap, as a function of its initial distance from the point. This allows the counts to be converted to an estimate of abundance in the survey region.We illustrated the methods using a lure survey of crossbillsLoxiaspp. in coniferous woodland in Scotland.Synthesis and applications.Two extensions of point transect sampling that use the same statistical methodology, lure point transects and trapping point transects, have been developed. Lure point transects extend the applicability of distance sampling to species that can be lured to a point, while trapping point transects potentially allow abundance estimation of species that can be trapped, with fewer resources needed than trapping webs and conventional mark–recapture methods.

Evaluation of trapping-web designs

The trapping web is a method for estimating the density and abundance of animal populations. A Monte Carlo simulation study is performed to explore performance of the trapping web for estimating animal density under a variety of web designs and animal behaviours. The trapping performs well when animals have home ranges, even if the home ranges are large relative to trap spacing. Webs should contain at least 90 traps. Trapping should continue for 5–7 occasions. Movement rates have little impact on density estimates when animals are confined to home ranges. Estimation is poor when animals do not have home ranges and movement rates are rapid. The trapping web is useful for estimating the density of animals that are hard to detect and occur at potentially low densities.

Comparison of two techniques to survey macropod abundance in an ecologically sensitive habitat.

THERE are many techniques available to measure the abundance of animal populations (e.g., Caughley 1977; Caughley and Grigg 1981; Southwell 1989; McCallum 2000; Buckland et al. 2001). A key point emphasised by each of these authors is that when choosing the most appropriate method(s) for measuring the abundance of animal populations, the manager or researcher must consider the ecological question(s) being asked. This in turn will determine what technique(s) will be most appropriate, what data are likely to be collected for analysis, and how these data will address the ecological question being asked. For the larger macropods, particularly Macropus spp., many of the techniques used to measure the abundance, and associated issues, have been reviewed (see Southwell 1989). Despite this, the applicability of these techniques has rarely been compared, particularly with respect to the observed variability in temporal counts.

Conservation and Disease

In developed countries over the past 50 years and more, a combination of better nutrition, better hygiene, antibiotics and other chemotherapeutic agents, and programs of immunization have almost eradicated morbidity and mortality resulting from infectious diseases. The smallpox virus is now extinct in the wild (and no conservationist mourned this act; our concerns change sign as we move from very large organisms to microorganisms). Scarlet fever and diphtheria, which carried off heroines in so many Victorian novels-and in Victorian real life-are rarely heard of today. Vaccination has removed polio from essentially all developed countries, and measles, whooping cough, rubella and other childhood infections seem on the road to local extinction in many. Whereas hookworm and other parasitic infections were endemic in the southern regions of the United States in the early years of this century, most people in developed countries today would react with horror to the thought of harboring a couple of intestinal or other parasites. Although heavy burdens of such parasites continue to afflict many people in developing countries, not the least of the reasons why HIV/AIDS so appalls us, I think, is that in developed countries we have come to believe a life free from any serious effects of viral, bacterial, protozoan or helminth infections is a natural state, to which we have some kind of entitlement. Nothing could be further from the truth. As emphasized by Haldane (1949), infectious diseases have undoubtedly been the main agents of morbidity and mortality (and thus the dominant selective forces) in human populations at least for the past 10,000 years. In combination with malnutrition, infectious diseases are still the main cause of the dramatic differences between survivorship curves in developed and developing countries (Bradley, 1974). To put it another way, current estimates are that 30% of HIV infections go on to produce death from AIDS (although this number may rise as longer runs of data accumulate) which can be compared with the 30% case-mortality associated with smallpox infections that were, until recently, endemic in most parts of the world. Given the conspicuous role that diseases have played, and in many parts of the world continue to play, in human demography, it is surprising that ecologists have given so little attention to the way diseases may affect the distribution and abundance of other animals and plants. Until recently, for example, ecology textbooks had chapters discussing how vertebrate and invertebrate predators may influence prey abundance, but in most cases you will search the index in vain for mention of infectious diseases. I think this is partly because ecologists find fourand six-legged predators more engaging, partly because pathogenic organisms (like decomposers, another category of organisms neglected by most ecologists) are relatively hard to see and thus to study, and partly because veterinarians and wildlife managers understandably tend to focus on individual sick animals rather than on population aspects of infection. The past few years have, however, seen an upsurge in efforts to document the effects that viral, bacterial, protozoan and helminth infections may have on the distribution and abundance of animal populations in the laboratory and-more importantly-in the field (for reviews, see Anderson and May, 1978, 1979 or Toft, 1986). These studies have many implications for conservation biology, some of which are widely recognized and others not. It therefore seemed a good idea to hold a symposium on and Disease at the first annual meeting for the Society for Conservation Biology, and to publish the four papers presented at that symposium in this issue of the journal. The first paper, by Marilyn Scott, reviews evidence for the ways in which infectious diseases may influence the ecology of animal populations. In particular, Scott gives

Parametric Models for Line‐Transect Estimators of Abundance

The estimation of the abundance of animal populations with the line—transect sampling method requires that a sighting model be postulated to represent the decreased probability of a sighting as its distance from the transect line increases. The development of parametric sighting models and estimation techniques is reviewed, and general procedures for variance estimation are given. Two new models and their corresponding abundance estimators are developed. The half—normal model provides a useful alternative to the widely used exponential model. The generalized exponential model contains the half—normal and exponential models as special cases and has the flexibility to account for a wide range of sighting phenomena. The new models are applied to transect surveys of porpoise schools and the results are related to sampling and ecological conditions. Criteria for model selection and transect design are discussed.

Patterns of Numerical Abundance of Animal Populations

Research Article| March 01 1969 Patterns of Numerical Abundance of Animal Populations Jerry L. Wilhm Jerry L. Wilhm Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (1969) 31 (3): 147–150. https://doi.org/10.2307/4442448 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Jerry L. Wilhm; Patterns of Numerical Abundance of Animal Populations. The American Biology Teacher 1 March 1969; 31 (3): 147–150. doi: https://doi.org/10.2307/4442448 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Copyright 1969 The National Association of Biology Teachers Article PDF first page preview Close Modal You do not currently have access to this content.

On the cyclic abundance of animal populations

On the cyclic abundance of animal populations

The Statisticaal Analysis of Creel-Census Data

An analysis of the yield of brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdnerii) per unit of fishing effort at Furnace Brook, Vermont, shows how modern statistical methods can be utilized to determine the significance of changes in the relative abundance of animal populations. The data cover the 5 years from 1936 to 1940 and the analysis of covariance employed shows that there was a significant decrease in the catch per unit of effort in 1939 which was attributed to the effects of severe floods caused by the hurricane in September of the previous year. This method of analysis, although useful for supplying a measure of relative abundance, fails to provide an estimate of the actual stock on hand. A method of estimating the total population based on the proportion of fish maturing and the number of mature fish counted in the spawning run is presented. A new method for estimating the size of animal populations from data on catch and effort has recently been developed by DeLury. When certain assumptions are made, the following relations hold:log C(t) = log (kN(O))—kE(t),where C(t) is the catch per unit of effort for a given time interval (t), E(t) is the total effort expended during the time interval (O, t), N(O) is the number of individuals at t=O, and, k is a constant describing the rate at which the catch per unit of effort decreases as the effort accumulates. The writer has developed a similar method, which would be much easier for biologists to use, based on the following equation:C(t) = kN(O) − kK(t),where K(t) is the total catch accumulated during the time interval (O, t), and k is a constant describing the rate at which the catch per unit of effort decreases as the catch accumulates. Data from the rainbow trout fishery at Paul Lake, British Columbia, obtained in 1932, show that both methods of estimation yield approximately the same result. The second method is suggested as an aid for fishery managers who wish to determine the size of their fish stocks. It requires that records be obtained concerning the catch and the fishing effort throughout the fishing season and that the proportion of the different age groups in the catch be determined. If sampling is used, then representative sampling methods are required. An example is given to show how the method may be used by fishery managers.