Bimodal population size distributions and biased gillnet sampling

2004 ◽  
Vol 61 (11) ◽  
pp. 2151-2157 ◽  
Author(s):  
Anders Gravbrøt Finstad ◽  
Ole Kristian Berg
Keyword(s):  
Sampling Method ◽  
Salvelinus Alpinus ◽  
Size Difference ◽  
Size Distributions ◽  
Abrupt Increase ◽  
Bimodal Size Distribution ◽  
Lower Mode ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Intermediate Size

Bimodal size distributions have been commonly observed in Arctic char (Salvelinus alpinus). We document an example of such bimodality caused solely by biased gillnet sampling. The observed bimodality was a direct artefact of the sampling method resulting from an abrupt increase in gillnet catchability of fish larger in total length than between 25 and 30 cm. Mean gillnet selectivity (catchability) of char in the upper mode of the observed bimodal size distribution was about 40 times higher than the corresponding value for char in the observed lower mode. Fish of intermediate size, lacking in the gillnet samples, were present in the population and readily obtainable by electrofishing. The observed size difference in gillnet vulnerability is likely to result from behavioural changes following ontogenetic niche shifts.

scholarly journals Ontogenetic niche shifts in dinosaurs influenced size, diversity and extinction in terrestrial vertebrates

2012 ◽  
Vol 8 (4) ◽  
pp. 620-623 ◽  
Author(s):  
Daryl Codron ◽  
Chris Carbone ◽  
Dennis W. H. Müller ◽  
Marcus Clauss
Keyword(s):  
Postnatal Ontogeny ◽  
Terrestrial Vertebrates ◽  
Terrestrial Vertebrate ◽  
Physiological Limits ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Size Diversity ◽  
Intermediate Size ◽  
The Impact ◽  
Land Vertebrates

Given the physiological limits to egg size, large-bodied non-avian dinosaurs experienced some of the most extreme shifts in size during postnatal ontogeny found in terrestrial vertebrate systems. In contrast, mammals—the other dominant vertebrate group since the Mesozoic—have less complex ontogenies. Here, we develop a model that quantifies the impact of size-specific interspecies competition on abundances of differently sized dinosaurs and mammals, taking into account the extended niche breadth realized during ontogeny among large oviparous species. Our model predicts low diversity at intermediate size classes (between approx. 1 and 1000 kg), consistent with observed diversity distributions of dinosaurs, and of Mesozoic land vertebrates in general. It also provides a mechanism—based on an understanding of different ecological and evolutionary constraints across vertebrate groups—that explains how mammals and birds, but not dinosaurs, were able to persist beyond the Cretaceous–Tertiary (K–T) boundary, and how post-K–T mammals were able to diversify into larger size categories.

scholarly journals Predation and associational refuge drive ontogenetic niche shifts in an arctiid caterpillar

Ecology ◽  
2015 ◽  
Vol 96 (1) ◽  
pp. 80-89 ◽  
Author(s):  
Patrick Grof-Tisza ◽  
Marcel Holyoak ◽  
Edward Antell ◽  
Richard Karban
Keyword(s):  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Ontogenetic Niche ◽  
Associational Refuge

Ontogenetic Niche Shifts, Predators, and Coexistence among Consumer Species

2013 ◽  
Author(s):  
André M. de Roos ◽  
Lennart Persson
Keyword(s):  
Alternative Stable States ◽  
Niche Partitioning ◽  
Stage Structure ◽  
Stable States ◽  
Stable Coexistence ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Ontogenetic Niche ◽  
Dependent Growth ◽  
Equal Population

This chapter considers how stage structure and ontogenetic niche shifts may affect the coexistence between two consumer species competing for two resources in the absence and presence of predators, and how ontogenetic niche shifts may give rise to alternative stable states. More specifically, the analysis will use techniques developed within the consumer-resource framework of Tilman (1982), including consumption and renewal vectors (Schellekens, de Roos, and Persson 2010). Tilman showed that stable coexistence between consumers feeding on the same two resources is possible if each consumer species feeds proportionally more on the resource that limits its own growth most. Stable coexistence is, however, also affected by the form of resource-dependent growth isoclines, which represent combinations of resource densities that lead to equal population growth of consumers. It is shown that ontogenetic niche shifts per se affect the form of resource-dependent growth isoclines, which in turn may lead to coexistence through niche partitioning. The chapter also discusses how predation may promote the performance of a species undergoing ontogenetic niche shifts even in the case where it is both the inferior competitor and the preferred prey of the predator.

Ontogenetic Niche Shifts

2013 ◽  
Author(s):  
André M. de Roos ◽  
Lennart Persson
Keyword(s):  
Life History ◽  
Extended Model ◽  
Full Model ◽  
Life History Stages ◽  
Ontogenetic Diet Shifts ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Limited Supply ◽  
Diet Shifts ◽  
Parameter Values

This chapter considers the consequences for community structure of ontogenetic diet shifts that involve the use of different resources in different life history stages, whereby these resources are in limited supply and are hence competed for by all individuals foraging on them. It explores the consequences of ontogenetic diet shifts using stage-structured biomass models that account for two basic resources, a stage-structured consumer population, for which we distinguish between juveniles and adults, and up to two unstructured predator populations. The most extended model is therefore closely related to the model analyzed in Chapter 5, except for the inclusion of an additional basic resource. The equations of the full model are summarized and default parameter values are listed.

Summary

2013 ◽  
Author(s):  
André M. de Roos ◽  
Lennart Persson
Keyword(s):  
Population Dynamics ◽  
Life History ◽  
General Framework ◽  
Community Effects ◽  
Present Volume ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Different Types ◽  
Emergent Community ◽  
Ontogenetic Niche

This chapter provides a summary of the topics covered by the present volume. The summary serves the purpose of clearly showing how different chapters fit together in a general framework with respect to model approaches as well as results obtained. Reading this summary chapter will show readers the different types of community modules that will be analyzed as well as provide a clear impression of the results and insights that presented in this book. Topics discussed include biomass overcompensation, ontogenetic (a)symmetry in energetics, emergent community effects of biomass overcompensation, ontogenetic niche shifts in consumer life history, ontogenetic niche shifts in predator life history, competition between consumers with and without ontogenetic niche shifts, and ontogenetic (a)symmetry in energetics and population dynamics.

14C Variations in Pre-Bomb Nearshore Habitats of the Florida Panhandle, USA

Radiocarbon ◽  
2015 ◽  
Vol 57 (3) ◽  
pp. 469-479 ◽  
Author(s):  
Carla S Hadden ◽  
Alexander Cherkinsky
Keyword(s):  
Northwest Coast ◽  
Short Term ◽  
Marine Gastropods ◽  
Nearshore Environments ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Radiocarbon Data ◽  
Florida Panhandle ◽  
Reservoir Age ◽  
Short Term Variability

This article presents radiocarbon data for known-age, pre-bomb marine gastropods, Busycon sinistrum and Strombus alatus, collected between AD 1924 and 1946 from nearshore environments of the Florida Panhandle, on the northern Gulf of Mexico. Δ14C was measured in whole crushed juvenile specimens (n = 7) and terminal edges of adult specimens (n = 6). A subsample of adult specimens (n = 3) was subjected to additional, intrashell sampling to observe short-term variability in 14C conditions. Δ14C values were consistent within and among B. sinistrum specimens, and we propose a reservoir age offset (ΔR) of −9 ± 25 14C yr for B. sinistrum from the northwest coast of Florida. S. alatus shells exhibited significant variability from one individual to another, and also within individual specimens. ΔR values for S. alatus range from −3 ± 30 to 659 ± 30 14C yr. These differences may result from a combination of factors, including subregional variability in inputs of 14C-depleted waters and life-history factors including mobility, mode of feeding, and ontogenetic niche shifts.

Growth Patterns in Bluegill (Lepomis macrochirus) and Pumpkinseed (L. gibbosus) Sunfish: Environmental Variation and the Importance of Ontogenetic Niche Shifts

1988 ◽  
Vol 45 (1) ◽  
pp. 17-26 ◽  
Author(s):  
Craig W. Osenberg ◽  
Earl E. Werner ◽  
Gary G. Mittelbach ◽  
Donald J. Hall
Keyword(s):  
Growth Rates ◽  
Lepomis Macrochirus ◽  
Growth Patterns ◽  
Adult Performance ◽  
Littoral Habitat ◽  
Ontogenetic Niche Shifts ◽  
Niche Shifts ◽  
Dependent Growth ◽  
Specific Growth Rates ◽  
Recent Experimental Work

Size-specific growth rates were determined for bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) sunfish collected between 1978 and 1985 in nine lakes in southwestern Michigan. Variation in growth rates was attributable to lake effects as well as an interaction between lake and year effects. Year effects explained none of the observed variation, suggesting that growth rates were influenced more by unique lake differences than by annual climatic differences. Analyses of the covariation in growth among different size-classes of bluegill and pumpkinseed revealed that small bluegill (< 55 mm standard length (SL)) and small pumpkinseed (< 40 mm SL) exhibited similar responses to environmental factors, while large bluegill (> 55 mm SL) and large pumpkinseed (> 50 mm SL) responded differently. These breaks in the growth patterns coincide with the sizes at which each species exhibits an ontogenetic shift in diet. Comparison of growth rates and resource densities suggests that the growth rates of the large fishes were food limited. Small fishes showed significant density-dependent growth. This correlative evidence for competition is in agreement with recent experimental work. We suggest that the competition between juvenile sunfishes is driven by the effects of adult resources on adult performance and the eventual recruitment of juveniles into the littoral habitat.

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