Hierarchical models improve the use of alligator abundance as an indicator

Farris, Seth C.; Waddle, J. Hardin; Hackett, Caitlin; Brandt, Laura A.; Mazzotti, Frank J.

doi:10.1016/j.ecolind.2021.108406

Cited by 3 publications

(1 citation statement)

References 42 publications

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“…Esto brinda una alternativa más robusta en comparación a los IAR calculados con la Ecuación 4. Los modelos N-mixtos se han utilizado para datos con trampas cámara (Zou et al 2019, Luo et al 2020, Farris et al 2021. Para comparar entre especies se pueden utilizar modelos N-mixtos (Yamaura et al 2016).…”

Section: Modelos De Abundancia N-mixtosunclassified

Índice de abundancia relativa y tasa de encuentro con trampas cámara

Mandujano

2024

MaNo

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El monitoreo de fauna silvestre se basa en conteos directos o indirectos de animales o sus rastros, en unidades de muestreo (cámaras, transectos, trampas, redes, grabadores, u otro). Los conteos por unidad o esfuerzo de muestreo se expresan como tasa de encuentro, tasa fotográfica, tasa de captura, etc. Cuando se asume que la tasa está relacionada con el tamaño poblacional, entonces es considerada como un índice de abundancia relativa (IAR). Los cuales son empleados como alternativa a las estimaciones absolutas de la abundancia o densidad. Los IAR son utilizados para monitorear el cambio de una población a través del tiempo, o bien para comparar poblaciones de la misma especie en localidades diferentes. Con el incremento en el uso de las cámaras trampa se ha popularizado el cálculo de los IAR para todas las especies fotografiadas en el área de estudio. Sin embargo, se debe tener precaución con esta interpretación ya que los IAR están sesgados por la detectabilidad que varía entre especies. En este artículo se 1) reviso las definiciones, los supuestos y las limitaciones de los IAR; 2) explica la diferencia conceptual entre los IAR y las tasas de encuentro; 3) enfatiza la importancia de la probabilidad de detección como factor que afecta a los conteos y por ende a las tasas de encuentro; 4) sugiere usar los IAR solo para comparar a la misma especie temporal y espacialmente, mientras que la tasa de encuentro usarla para comparar entre especies; y 5) sugiero algunas alternativas de análisis estadísticos basados en modelos jerárquicos.

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Section: Modelos De Abundancia N-mixtosunclassified

Índice de abundancia relativa y tasa de encuentro con trampas cámara

Mandujano

2024

MaNo

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Trends in American Alligator Pods in Arthur R. Marshall Loxahatchee National Wildlife Refuge

Brandt

2024

Journal of Fish and Wildlife Management

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Alligators are an important component of the Greater Everglades serving as ecosystem engineers, predator, prey, and are tightly tied to water depth patterns. Because of their importance to ecosystem function and link to hydrology, alligators are an ecological indicator for Everglades restoration. I used data from fall night-time spotlight surveys of alligators in the Arthur R. Marshall Loxahatchee National Wildlife Refuge to describe the trend in number of hatchling pods from 1998 to 2021 and relate that trend to hydrologic parameters hypothesized to influence alligator production. I used an information-theoretic approach to evaluate 14 models created from combinations of year of observation and three hydrologic variables: average and range in water depth from 16 April of the previous year to 15 April of the nesting year (breeding potential window) and average water depth from 16 April to 31 May of the nesting year (courtship and mating window). Number of pods ranged from 16 in 1998 to 0 in 2011. Each of the four top models included year and one or more of the hydrologic variables as predictors and explained 26-34% (D-squared) of the variation in number of pods. Year was the predictor for which the 95% confidence interval did not contain zero and indicated a declining trend (-3% to -8%; 95% confidence interval). All hydrologic variables were included in the top models indicating they contribute some information toexplaining the trend; however, contrary to my hypotheses, there was not a clear relationship between any of the hydrologic variables and number of alligator pods. My hypotheses were based on information synthesized in the Alligator Production Suitability Index model being used in Everglades restoration planning and my results suggest that additional refinement of that model is warranted.

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N-mixture models provide informative crocodile (Crocodylus moreletii) abundance estimates in dynamic environments

Barão-Nóbrega

González-Jaurégui

Jehle

2022

PeerJ

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Estimates of animal abundance provide essential information for population ecological studies. However, the recording of individuals in the field can be challenging, and accurate estimates require analytical techniques which account for imperfect detection. Here, we quantify local abundances and overall population size of Morelet’s crocodiles (Crocodylus moreletii) in the region of Calakmul (Campeche, Mexico), comparing traditional approaches for crocodylians (Minimum Population Size—MPS; King’s Visible Fraction Method—VFM) with binomial N-mixture models based on Poisson, zero-inflated Poisson (ZIP) and negative binomial (NB) distributions. A total of 191 nocturnal spotlight surveys were conducted across 40 representative locations (hydrologically highly dynamic aquatic sites locally known as aguadas) over a period of 3 years (2017–2019). Local abundance estimates revealed a median of 1 both through MPS (min–max: 0–89; first and third quartiles, Q1–Q3: 0–7) and VFM (0–112; Q1–Q3: 0–9) non-hatchling C. moreletii for each aguada, respectively. The ZIP based N-mixture approach shown overall superior confidence over Poisson and NB, and revealed a median of 6 ± 3 individuals (min = 0; max = 120 ± 18; Q1 = 0; Q3 = 18 ± 4) jointly with higher detectabilities in drying aguadas with low and intermediate vegetation cover. Extrapolating these inferences across all waterbodies in the study area yielded an estimated ~10,000 (7,000–11,000) C. moreletii present, highlighting Calakmul as an important region for this species. Because covariates enable insights into population responses to local environmental conditions, N-mixture models applied to spotlight count data result in particularly insightful estimates of crocodylian detection and abundance.

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Hierarchical models improve the use of alligator abundance as an indicator

Cited by 3 publications

References 42 publications

Índice de abundancia relativa y tasa de encuentro con trampas cámara

Índice de abundancia relativa y tasa de encuentro con trampas cámara

Trends in American Alligator Pods in Arthur R. Marshall Loxahatchee National Wildlife Refuge

N-mixture models provide informative crocodile (Crocodylus moreletii) abundance estimates in dynamic environments

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