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Effects of life-state on detectability in a demographic study of the terrestrial orchid Cleistes bifaria / Marc Kéry in Journal of ecology, 91 (2003) 

Public Citation [article]  inJournal of ecology > 91 (2003) . - 265-273 Titre : Effects of life-state on detectability in a demographic study of the terrestrial orchid Cleistes bifaria Type de document : Numérique Auteurs : Marc Kéry ; Katharine B. Gregg Année de publication : 2003 Article en page(s) : 265-273 Langues : Français (fre) Mots-clés : Cleistes bifaria  Cleistesiopsis bifaria Résumé : 1. Most plant demographic studies follow marked individuals in permanent plots. Plots tend to be small, so detectability is assumed to be one for every individual. However, detectability could be affected by factors such as plant traits, time, space, observer, previous detection, biotic interactions, and especially by life-state. 2. We used a double-observer survey and closed population capture-recapture modelling to estimate state-specific detectability of the orchid Cleistes bifaria in a long-term study plot of 41.2 m2. Based on AICc model selection, detectability was different for each life-state and for tagged vs. previously untagged plants. There were no differences in detectability between the two observers. 3. Detectability estimates (SE) for one-leaf vegetative, two-leaf vegetative, and flowering/fruiting states correlated with mean size of these states and were 0.76 (0.05), 0.92 (0.06), and 1 (0.00), respectively, for previously tagged plants, and 0.84 (0.08), 0.75 (0.22), and 0 (0.00), respectively, for previously untagged plants. (We had insufficient data to obtain a satisfactory estimate of previously untagged flowering plants). 4. Our estimates are for a medium-sized plant in a small and intensively surveyed plot. It is possible that detectability is even lower for larger plots and smaller plants or smaller life-states (e.g. seedlings) and that detectabilities < I are widespread in plant demographic studies. 5. State-dependent detectabilities are especially worrying since they will lead to a size- or state-biased sample from the study plot. Failure to incorporate detectability into demographic estimation methods introduces a bias into most estimates of population parameters such as fecundity, recruitment, mortality, and transition rates between life-states. We illustrate this by a simple example using a matrix model, where a hypothetical population was stable but, due to imperfect detection, wrongly projected to be declining at a rate of 8% per year. 6. Almost all plant demographic studies are based on models for discrete states. State and size are important predictors both for demographic rates and detectability. We suggest that even in studies based on small plots, state- or size-specific detectability should be estimated at least at some point to avoid biased inference about the dynamics of the population sampled. Identifiant : DOI : 10.1046/j.1365-2745.2003.00759.x Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=155757 Kéry, Marc, Gregg, Katharine B. 2003 Effects of life-state on detectability in a demographic study of the terrestrial orchid Cleistes bifaria. Journal of ecology, 91: 265-273.

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Consultable Article (2003) URL

Reduced fecundity and offspring performance in small populations of declining grassland Primula veris and Gentiana lutea / Marc Kéry (2000) 

Public Citation est un tiré à part de 88 (3) - 2000 (Journal of ecology) Titre : Reduced fecundity and offspring performance in small populations of declining grassland Primula veris and Gentiana lutea Type de document : Tiré à part de revue Auteurs : Marc Kéry ; Diethart Matthies ; Hans-Heinrich Spillmann Année de publication : 2000 Importance : 17-30 Langues : Français (fre) Catégories : [CBNPMP-Thématique] Démographie [CBNPMP-Thématique] Germination [CBNPMP-Thématique] Stratégie de production de semences (fécondité) Mots-clés : Gentiana lutea L.  Primula veris L. Résumé : 1 We studied reproduction and offspring performance in relation to population size in the declining self-incompatible perennials Primula veris and Gentiana lutea. In both species, reproduction was strongly reduced in small populations, where plants produced fewer seeds per fruit and per plant. Total seed mass per plant was higher in large populations, but individual seeds were smaller, indicating a trade-off between seed number and size. Reproduction was depressed most strongly in populations consisting of less than c. 200 (P. veris) and c. 500 plants (G. lutea), respectively. 2 The inclusion of plant size (an integrated measure of habitat quality) in the statistical models did not change the relationships between fecundity and population size. Pollen limitation or inbreeding depression in small populations are therefore more likely explanations for these patterns than is habitat quality. 3 Germination rate and survival of seedlings in a common environment was not related to population size in either species, although P. veris developed into larger rosettes when seeds were derived from large populations. This suggests that inbreeding depression occurs in small populations of P. veris. 4 In a factorial fertilizer-by-competition experiment with P. veris, offspring from larger populations grew significantly larger and responded more strongly to fertilizer. For this declining species genetic deterioration as a result of habitat fragmentation may therefore aggravate the effects of environmental changes such as habitat eutrophication. 5 Our results suggest that small populations may face an increased short-term risk of extinction because of reduced reproduction, and an increased long-term risk because they are less able to respond to environmental changes. Identifiant : DOI : 10.1046/j.1365-2745.2000.00422.x Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=130653 Kéry, Marc, Matthies, Diethart, Spillmann, Hans-Heinrich 2000 Reduced fecundity and offspring performance in small populations of declining grassland Primula veris and Gentiana lutea. Journal of ecology, 88(3) : 17-30.

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Code-barres	Cote	Support	Localisation	Section	Disponibilité
10761	K	Tiré à part	Centre de documentation	Tirés à part	Consultable

Documents numériques

Consultable Article (2000) URL