The problem of unequal catchability in mark–recapture estimation of small mammal populations

1983 ◽  
Vol 61 (4) ◽  
pp. 922-927 ◽  
Author(s):  
G. M. Jolly ◽  
J. M. Dickson
Keyword(s):  
Population Size ◽  
Small Mammal ◽  
Negative Bias ◽  
Mark Recapture ◽  
Complete Enumeration ◽  
Open Population ◽  
Minimum Number ◽  
Future Work

The problem of unequal catchability among individuals in an open population is discussed in regard to estimates of population size. Properties of the Jolly–Seber (J–S) estimate are clarified and comparisons are made with minimum number alive (MNA) techniques which attempt complete enumeration of the population. The MNA is shown to be seriously biased under the assumption of equal catchability and to have a proportionately much larger negative bias than the J–S estimate under unequal catchability. Suggestions are made for future work.

The closed-subpopulation method and estimation of population size from mark-recapture and ancillary data

2000 ◽  
Vol 78 (2) ◽  
pp. 320-326 ◽  
Author(s):  
Frank AM Tuyttens
Keyword(s):  
Population Size ◽  
Ancillary Data ◽  
Mark Recapture ◽  
Animal Populations ◽  
Accuracy And Precision ◽  
Population Size Estimates ◽  
Minimum Number ◽  
Flexible Framework ◽  
And Performance ◽  
Better Than

The algebraic relationships, underlying assumptions, and performance of the recently proposed closed-subpopulation method are compared with those of other commonly used methods for estimating the size of animal populations from mark-recapture records. In its basic format the closed-subpopulation method is similar to the Manly-Parr method and less restrictive than the Jolly-Seber method. Computer simulations indicate that the accuracy and precision of the population estimators generated by the basic closed-subpopulation method are almost comparable to those generated by the Jolly-Seber method, and generally better than those of the minimum-number-alive method. The performance of all these methods depends on the capture probability, the number of previous and subsequent trapping occasions, and whether the population is demographically closed or open. Violation of the assumption of equal catchability causes a negative bias that is more pronounced for the closed-subpopulation and Jolly-Seber estimators than for the minimum-number-alive. The closed-subpopulation method provides a simple and flexible framework for illustrating that the precision and accuracy of population-size estimates can be improved by incorporating evidence, other than mark-recapture data, of the presence of recognisable individuals in the population (from radiotelemetry, mortality records, or sightings, for example) and by exploiting specific characteristics of the population concerned.

Comment—Revised estimates of the bias in the 'minimum number alive' estimator

1992 ◽  
Vol 70 (3) ◽  
pp. 628-631 ◽  
Author(s):  
Murray Efford
Keyword(s):  
Computer Simulation ◽  
Population Size ◽  
Coefficient Of Variation ◽  
Population Estimate ◽  
Negative Bias ◽  
Highly Sensitive ◽  
Minimum Number ◽  
Simulation Results ◽  
Open Populations ◽  
Minimum Numbers

The computer simulation results of Hilborn et al. (R. Hilborn, J. A. Redfield, and C. J. Krebs. 1976. Can. J. Zool. 54: 1019–1024) regarding the bias of the 'minimum number alive' estimator of population size are shown to be in error. Minimum numbers alive are approximately twice as biased as estimated by these authors: for five species of Microtus the negative bias is estimated as 24–45% instead of 10–18%. 'Minimum number alive' differs from the Jolly–Seber population estimate in being particularly sensitive to mean trappability when the coefficient of variation of trappability is constant. Both population estimators are highly sensitive to reduced trappability of unmarked animals. The Jolly–Seber estimator remains the method of choice for open populations, especially if the coefficient of variation in trappability can be minimized.

Live-trapping of the northern hairy-nosed wombat (Lasiorhinus krefftii): population-size estimates and effects on individuals

1995 ◽  
Vol 22 (6) ◽  
pp. 741 ◽  
Author(s):  
SD Hoyle ◽  
AB Horsup ◽  
CN Johnson ◽  
DG Crossman ◽  
H McCallum
Keyword(s):  
Population Size ◽  
Confidence Limit ◽  
Mark Recapture ◽  
Population Size Estimate ◽  
Live Trapping ◽  
Population Size Estimates ◽  
Minimum Number ◽  
Estimate Population Size ◽  
Second Period ◽  
Size Estimates

The northern hairy-nosed wombat, one of the most endangered large mammals known, occurs only in Epping Forest National Park, central Queensland. The results of a 3-stage trapping programme, carried out between 1985 and 1993, were used to estimate population size by means of three separate modelling approaches: minimum number alive (MNA), mark-recapture, and trapping effort. Trapping procedure varied among sessions, and each estimator was applied to sessions only where its use was appropriate. The population-size estimate for 1985-86 was 67 (trap effort) with MNA of 58; for 1988-89 it was 62 (Jolly-Seber mark-recapture estimate), with MNA of 48 and upper 95% confidence limit of 77; and for 1993 it was 65 (Chao mark-recapture and trap effort), with MNA of 43 and upper 95% confidence limit of 186 (Chao mark-recapture). No population trends were observed, although variability in estimates and wide confidence intervals meant that power to do so was limited. Trapping affected the health and behaviour of wombats. Animals that were trapped twice within 10 nights lost an average of 0.62 kg (P = 0.006) between captures. Wombats that were trapped twice within the first four nights of traps being set on a burrow showed less weight loss than those trapped for the second time after 5-7 nights (0.23 kg v. 1.54 kg). The effects of trapping appeared to remain with animals for some time, since animals trapped twice more than 30 nights apart and within six months weighed an average of 0.5 kg less (P = 0.013) on second capture. When areas were trapped twice in succession with a 3-week gap, population-size estimates were lower for the second period of trapping. Thus, some wombats may have temporarily left areas disturbed by trapping. The deleterious impact of trapping may be reduced by restricting trapping to periods of four nights. Trapping effectiveness may be increased by minimising disturbance immediately before trapping and by moving traps between periods of trapping.

scholarly journals Challenges and opportunities for monitoring wild Nile crocodiles with scute mark-recapture photography

Koedoe ◽  
2018 ◽  
Vol 60 (1) ◽  
Author(s):  
Bernard W.T. Coetzee ◽  
Sam M. Ferreira ◽  
Kristine Maciejewski
Keyword(s):  
Conservation Status ◽  
Field Conditions ◽  
High Turnover ◽  
Mark Recapture ◽  
Non Invasive ◽  
Open Population ◽  
Challenges And Opportunities ◽  
In Captivity ◽  
In The Wild

The global conservation status of Nile crocodiles (Crocodylus niloticus) was last assessed in 1996. The species presents particular difficulty in monitoring because it can be cryptic, require expertise to handle, and caudal tail tags and transmitters are often lost. Some studies advocate mark-recapture techniques based on photograph identification of the unique scute markings of crocodile tails as a non-invasive means of monitoring their populations. Researchers developed this method with crocodiles in captivity. In this study, we test the technique under field conditions by monitoring crocodiles from 2015 to 2017 in the Sunset Dam in the Kruger National Park. Using a Cormack-Jolly-Seber open population model, we found that the dam may host 15–30 individuals, but that there is a high turnover of individuals and much uncertainty in model outputs. The dam’s population thus has high rates of immigration and emigration. The method proved challenging under field conditions, as there was bias in identifying scute markings consistently. The efficient use of the method requires an exceptional quality of photographic equipment. Animal crypsis, however, remains an issue. In this study, we discuss how to improve the mark-recapture photography methodology, especially to adapt the technique for citizen science initiatives.Conservation implications: Using scute mark-recapture photography presents challenges under field conditions. These challenges require innovative, practical and analytical solutions to successfully use the technique before monitoring programmes, aimed at ensuring the persistence of crocodiles in the wild, can be implemented.

Evaluating Live trapping and Camera-based Indices of Small Mammal Density

2021 ◽  
Author(s):  
Mitchell Alan Parsons ◽  
ALISHIA ORLOFF ◽  
Laura Prugh
Keyword(s):  
Small Mammal ◽  
Abundant Species ◽  
Monitoring Methods ◽  
Density Estimates ◽  
Full Dataset ◽  
Live Trapping ◽  
Minimum Number ◽  
Capture Recapture ◽  
Two Indices ◽  
Best Fit

Density estimates are integral to wildlife management, but they can be costly to obtain. Indices of density may provide efficient alternatives, but calibration is needed to ensure the indices accurately reflect density. We evaluated several indices of small mammal density using live trapping and motion-activated cameras in Washington’s Cascade Mountains. We used linear regression to compare spatially-explicit capture recapture density estimates of mice, voles, and chipmunks to four indices. Two indices were based on live trapping (minimum number alive and number of captures per 100 trap nights) and two indices were based on photos from motion-activated cameras (proportion of cameras detecting a species and the number of independent detections). We evaluated how the accuracy of trap-based indices increased with trapping effort using subsets of the full dataset (n = 7 capture occasions per site). Most indices provided reliable indicators of small mammal density, and live trapping indices (R2=0.64 – 0.98) outperformed camera-based indices (R2=0.24 – 0.86). All indices performed better for more abundant species. The effort required to estimate each index varied, and indices that required more effort performed better. These findings should help managers, conservation practitioners, and researchers select small mammal monitoring methods that best fit their needs.

scholarly journals About rats and jackfruit trees: modeling the carrying capacity of a Brazilian Atlantic Forest spiny-rat Trinomys dimidiatus (Günther, 1877) – Rodentia, Echimyidae – population with varying jackfruit tree (Artocarpus heterophyllus L.) abundances

2015 ◽  
Vol 75 (1) ◽  
pp. 208-215 ◽  
Author(s):  
JHF Mello ◽  
TP Moulton ◽  
DSL Raíces ◽  
HG Bergallo
Keyword(s):  
Mathematical Model ◽  
Population Size ◽  
Seed Production ◽  
Atlantic Forest ◽  
Small Mammal ◽  
Carrying Capacity ◽  
Real Data ◽  
Brazilian Atlantic Forest ◽  
Artocarpus Heterophyllus ◽  
Small Mammal Community

We carried out a six-year study aimed at evaluating if and how a Brazilian Atlantic Forest small mammal community responded to the presence of the invasive exotic species Artocarpus heterophyllus, the jackfruit tree. In the surroundings of Vila Dois Rios, Ilha Grande, RJ, 18 grids were established, 10 where the jackfruit tree was present and eight were it was absent. Previous results indicated that the composition and abundance of this small mammal community were altered by the presence and density of A. heterophyllus. One observed effect was the increased population size of the spiny-rat Trinomys dimidiatus within the grids where the jackfruit trees were present. Therefore we decided to create a mathematical model for this species, based on the Verhulst-Pearl logistic equation. Our objectives were i) to calculate the carrying capacity K based on real data of the involved species and the environment; ii) propose and evaluate a mathematical model to estimate the population size of T. dimidiatus based on the monthly seed production of jackfruit tree, Artocarpus heterophyllus and iii) determinate the minimum jackfruit tree seed production to maintain at least two T. dimidiatus individuals in one study grid. Our results indicated that the predicted values by the model for the carrying capacity K were significantly correlated with real data. The best fit was found considering 20~35% energy transfer efficiency between trophic levels. Within the scope of assumed premises, our model showed itself to be an adequate simulator for Trinomys dimidiatus populations where the invasive jackfruit tree is present.

scholarly journals Genetic mark‐recapture analysis of winter faecal pellets allows estimation of population size in Sage Grouse Centrocercus urophasianus

Ibis ◽  
2019 ◽  
Vol 162 (3) ◽  
pp. 749-765 ◽  
Author(s):  
Jessica E. Shyvers ◽  
Brett L. Walker ◽  
Sara J. Oyler‐McCance ◽  
Jennifer A. Fike ◽  
Barry R. Noon
Keyword(s):  
Population Size ◽  
Centrocercus Urophasianus ◽  
Sage Grouse ◽  
Mark Recapture ◽  
Faecal Pellets
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