Methods in Ecology and Evolution Volume 3, Issue 2, pages 245–256, April 2012
Summary
1. Plant growth is a fundamental ecological process, integrating across scales from ph... more Summary
1. Plant growth is a fundamental ecological process, integrating across scales from physiology to community dynamics and ecosystem properties. Recent improvements in plant growth modelling have allowed deeper understanding and more accurate predictions for a wide range of ecological issues, including competition among plants, plant–herbivore interactions and ecosystem functioning.
2. One challenge in modelling plant growth is that, for a variety of reasons, relative growth rate (RGR) almost universally decreases with increasing size, although traditional calculations assume that RGR is constant. Nonlinear growth models are flexible enough to account for varying growth rates.
3. We demonstrate a variety of nonlinear models that are appropriate for modelling plant growth and, for each, show how to calculate function-derived growth rates, which allow unbiased comparisons among species at a common time or size. We show how to propagate uncertainty in estimated parameters to express uncertainty in growth rates. Fitting nonlinear models can be challenging, so we present extensive worked examples and practical recommendations, all implemented in R.
4. The use of nonlinear models coupled with function-derived growth rates can facilitate the testing of novel hypotheses in population and community ecology. For example, the use of such techniques has allowed better understanding of the components of RGR, the costs of rapid growth and the linkage between host and parasite growth rates. We hope this contribution will demystify nonlinear modelling and persuade more ecologists to use these techniques.
Millions of birds migrate each year between breeding grounds and overwintering areas. Migration b... more Millions of birds migrate each year between breeding grounds and overwintering areas. Migration behavior is influenced by a number of factors: day length, physiological and genetic factors, the magnetic compass, population dynamics, and weather and climatic conditions. Historical and current data on avian migration are of broad scientific value. Most of information on avian migration is presented in form of summary statistics (e.g., duration of migration, number of individuals, trend line over years) in published studies, but original data sets are not readily available. Here, we describe the first open-source archive on visible diurnal spring migration in Central Europe. The database comprises the records of a systematic field study, which covers 35541 records of migrating birds for more than 138000 specimens of 96 species. Data were collected during the spring periods of 1984, 1985, and 1986. Bird census was conducted at the tip of the Höri peninsula in Lake Constance, Germany (north of the Alps: 47°41′49.11″ N, 9°00′21.52″ E). Migrating birds were counted from the beginning of March to the beginning of May each morning using fine-grained 15-min intervals. Flock size, migration heading, and weather conditions are provided for each species, e.g., for the European Chaffinch Fringilla coelebs. In all three years we found evidence that Chaffinches ceased to migrate to northeastern and eastern direction at the end of the observation period. The migration pattern of two thrush species (Turdus merula and T. viscivorus) is also presented in more detail. Turdus merula had its migration peak always early in the morning, whereas migration of T. viscivorus was recorded from the early morning onward, with a peak at late morning to noon. Migration records are also documented for species that are generally believed to be resident birds in the inland of Central Europe (e.g., Streptopelia decaocto, Parus palustris, Certhia brachydactyla, Pica pica). Our archive might be of significance for studying patterns of daily migration, e.g., the effect of weather on spring migration intensity and for methodological studies on the same issue.
Plants stand still and interact with their immediate neighbors. Theory has shown that the distanc... more Plants stand still and interact with their immediate neighbors. Theory has shown that the distances over which these interactions occur may have important consequences for population and community dynamics. In particular, if intraspecific competition occurs over longer distances than interspecific competition (heteromyopia), coexistence can be promoted. We examined how intraspecific and interspecific competition scales with neighbor distance in a target‐neighbor greenhouse competition experiment. Individuals from co‐occurring forbs from calcareous grasslands were grown in isolation and with single conspecific or heterospecific neighbors at distances of 5, 10, or 15 cm (Plantago lanceolata vs. Plantago media and Hieracium pilosella vs. Prunella grandiflora). Neighbor effects were strong and declined with distance. Interaction distances varied greatly within and between species, but we found no evidence for heteromyopia. Instead, neighbor identity effects were mostly explained by relative size differences between target and neighbor. We found a complex interaction between final neighbor size and identity such that neighbor identity may become important only as the neighbor becomes very large compared with the target individual. Our results suggest that species‐specific size differences between neighboring individuals determine both the strength of competitive interactions and the distance over which these interactions occur.
Methods in Ecology and Evolution Volume 3, Issue 2, pages 245–256, April 2012
Summary
1. Plant growth is a fundamental ecological process, integrating across scales from ph... more Summary
1. Plant growth is a fundamental ecological process, integrating across scales from physiology to community dynamics and ecosystem properties. Recent improvements in plant growth modelling have allowed deeper understanding and more accurate predictions for a wide range of ecological issues, including competition among plants, plant–herbivore interactions and ecosystem functioning.
2. One challenge in modelling plant growth is that, for a variety of reasons, relative growth rate (RGR) almost universally decreases with increasing size, although traditional calculations assume that RGR is constant. Nonlinear growth models are flexible enough to account for varying growth rates.
3. We demonstrate a variety of nonlinear models that are appropriate for modelling plant growth and, for each, show how to calculate function-derived growth rates, which allow unbiased comparisons among species at a common time or size. We show how to propagate uncertainty in estimated parameters to express uncertainty in growth rates. Fitting nonlinear models can be challenging, so we present extensive worked examples and practical recommendations, all implemented in R.
4. The use of nonlinear models coupled with function-derived growth rates can facilitate the testing of novel hypotheses in population and community ecology. For example, the use of such techniques has allowed better understanding of the components of RGR, the costs of rapid growth and the linkage between host and parasite growth rates. We hope this contribution will demystify nonlinear modelling and persuade more ecologists to use these techniques.
Millions of birds migrate each year between breeding grounds and overwintering areas. Migration b... more Millions of birds migrate each year between breeding grounds and overwintering areas. Migration behavior is influenced by a number of factors: day length, physiological and genetic factors, the magnetic compass, population dynamics, and weather and climatic conditions. Historical and current data on avian migration are of broad scientific value. Most of information on avian migration is presented in form of summary statistics (e.g., duration of migration, number of individuals, trend line over years) in published studies, but original data sets are not readily available. Here, we describe the first open-source archive on visible diurnal spring migration in Central Europe. The database comprises the records of a systematic field study, which covers 35541 records of migrating birds for more than 138000 specimens of 96 species. Data were collected during the spring periods of 1984, 1985, and 1986. Bird census was conducted at the tip of the Höri peninsula in Lake Constance, Germany (north of the Alps: 47°41′49.11″ N, 9°00′21.52″ E). Migrating birds were counted from the beginning of March to the beginning of May each morning using fine-grained 15-min intervals. Flock size, migration heading, and weather conditions are provided for each species, e.g., for the European Chaffinch Fringilla coelebs. In all three years we found evidence that Chaffinches ceased to migrate to northeastern and eastern direction at the end of the observation period. The migration pattern of two thrush species (Turdus merula and T. viscivorus) is also presented in more detail. Turdus merula had its migration peak always early in the morning, whereas migration of T. viscivorus was recorded from the early morning onward, with a peak at late morning to noon. Migration records are also documented for species that are generally believed to be resident birds in the inland of Central Europe (e.g., Streptopelia decaocto, Parus palustris, Certhia brachydactyla, Pica pica). Our archive might be of significance for studying patterns of daily migration, e.g., the effect of weather on spring migration intensity and for methodological studies on the same issue.
Plants stand still and interact with their immediate neighbors. Theory has shown that the distanc... more Plants stand still and interact with their immediate neighbors. Theory has shown that the distances over which these interactions occur may have important consequences for population and community dynamics. In particular, if intraspecific competition occurs over longer distances than interspecific competition (heteromyopia), coexistence can be promoted. We examined how intraspecific and interspecific competition scales with neighbor distance in a target‐neighbor greenhouse competition experiment. Individuals from co‐occurring forbs from calcareous grasslands were grown in isolation and with single conspecific or heterospecific neighbors at distances of 5, 10, or 15 cm (Plantago lanceolata vs. Plantago media and Hieracium pilosella vs. Prunella grandiflora). Neighbor effects were strong and declined with distance. Interaction distances varied greatly within and between species, but we found no evidence for heteromyopia. Instead, neighbor identity effects were mostly explained by relative size differences between target and neighbor. We found a complex interaction between final neighbor size and identity such that neighbor identity may become important only as the neighbor becomes very large compared with the target individual. Our results suggest that species‐specific size differences between neighboring individuals determine both the strength of competitive interactions and the distance over which these interactions occur.
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Papers by Deborah Vogt
1. Plant growth is a fundamental ecological process, integrating across scales from physiology to community dynamics and ecosystem properties. Recent improvements in plant growth modelling have allowed deeper understanding and more accurate predictions for a wide range of ecological issues, including competition among plants, plant–herbivore interactions and ecosystem functioning.
2. One challenge in modelling plant growth is that, for a variety of reasons, relative growth rate (RGR) almost universally decreases with increasing size, although traditional calculations assume that RGR is constant. Nonlinear growth models are flexible enough to account for varying growth rates.
3. We demonstrate a variety of nonlinear models that are appropriate for modelling plant growth and, for each, show how to calculate function-derived growth rates, which allow unbiased comparisons among species at a common time or size. We show how to propagate uncertainty in estimated parameters to express uncertainty in growth rates. Fitting nonlinear models can be challenging, so we present extensive worked examples and practical recommendations, all implemented in R.
4. The use of nonlinear models coupled with function-derived growth rates can facilitate the testing of novel hypotheses in population and community ecology. For example, the use of such techniques has allowed better understanding of the components of RGR, the costs of rapid growth and the linkage between host and parasite growth rates. We hope this contribution will demystify nonlinear modelling and persuade more ecologists to use these techniques.
1. Plant growth is a fundamental ecological process, integrating across scales from physiology to community dynamics and ecosystem properties. Recent improvements in plant growth modelling have allowed deeper understanding and more accurate predictions for a wide range of ecological issues, including competition among plants, plant–herbivore interactions and ecosystem functioning.
2. One challenge in modelling plant growth is that, for a variety of reasons, relative growth rate (RGR) almost universally decreases with increasing size, although traditional calculations assume that RGR is constant. Nonlinear growth models are flexible enough to account for varying growth rates.
3. We demonstrate a variety of nonlinear models that are appropriate for modelling plant growth and, for each, show how to calculate function-derived growth rates, which allow unbiased comparisons among species at a common time or size. We show how to propagate uncertainty in estimated parameters to express uncertainty in growth rates. Fitting nonlinear models can be challenging, so we present extensive worked examples and practical recommendations, all implemented in R.
4. The use of nonlinear models coupled with function-derived growth rates can facilitate the testing of novel hypotheses in population and community ecology. For example, the use of such techniques has allowed better understanding of the components of RGR, the costs of rapid growth and the linkage between host and parasite growth rates. We hope this contribution will demystify nonlinear modelling and persuade more ecologists to use these techniques.