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Modelling spatial and temporal species distribution in the Baltic Sea phytobenthic zone
Stockholm University, Faculty of Science, Department of Systems Ecology. (Marine Ecology)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Statistical modelling is often used to relate the presence or abundance of species to environmental predictors, thereby providing a basis for predictive mapping of species or biodiversity. The variables included must thus be relevant and reflect actual changes in the environment. Therefore, the quantification of species–environment relationships is an important aspect of predictive modelling.

This thesis examines how phytobenthic species or communities in the Baltic Sea relate to environmental gradients, and if different aspects of phytobenthic species distribution in the Baltic Sea could be explained by spatial or temporal variation in environmental factors. Predictive distribution modelling usually focuses on how environmental variables control the distribution of species or communities. Thus the relative weight of the predictor variables on different scales is of importance. In this thesis, I show that the relative importance of environmental variables depends both on geographic scale and location, and that it also differs between species or species groups.

There are no simple explanations to the temporal variability in species occurrence. I here show that the temporal changes in species distribution within the phytobentic zone varies in a spatial context. I also try to find temporal and spatio-temporal patterns in species distribution that could be related to changes in climate or anthropogenic disturbance. However, the findings in this thesis suggest that single factor explanations are insufficient for explaining large-scale changes in species distribution. A greater understanding of the relationship between species and their environment will lead to the development of more sensitive models of species distributions. The predictions can be used to visualise spatial changes in the distribution of plant and animal communities over time.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University , 2011. , 38 p.
Keyword [en]
species distribution modelling, niche, gradient, prediction, environmental factors, phytobenthos, scale
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-54269ISBN: 978-91-7447-230-1 (print)OAI: oai:DiVA.org:su-54269DiVA: diva2:393422
Public defence
2011-03-04, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 09:30 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.Available from: 2011-02-10 Created: 2011-01-27 Last updated: 2011-01-31Bibliographically approved
List of papers
1. Spatial predictions of Baltic phytobenthic communities: Measuring robustness of generalized additive models based on transect data
Open this publication in new window or tab >>Spatial predictions of Baltic phytobenthic communities: Measuring robustness of generalized additive models based on transect data
2008 (English)In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 74, no Supplement 1, S86-S96 p.Article in journal (Refereed) Published
Abstract [en]

The spatial distributions of benthic surface sediments and phytobenthic plant species were modelled at a high spatial resolution using generalized additive models together with field data from diving transects. The efficiency of different modelling options was validated using independent datasets, and model fit versus predictive power was analysed. For rock/boulder, sand and mud/clay increasing complexity of the model resulted in higher Reciever Operating Characteristics (ROC) values for the model fit, but lower ROC values for the independent validation. The same pattern was found for hard substrate algae species, whereas it was not true for the rooted plant species. As high model ROC values were often found to be connected to low predictive power of the models, this implies that internal model validation results should be treated cautiously. In general, the models should be kept simple, as the performance of the explanation model increases with increasing complexity, while the predictive power of the model generally decreases. Only by using external validation datasets, the true predictive capacity of an explanation model can be reliably measured, as internal validation schemes tend to over-estimate model performance. Our results also indicate that the Akaike Information Criterion is a more reliable model selection method than Cross-selection when there are few predictor variables.

Keyword
Spatial distribution, GAM, AIC, Cross-selection, Phytobenthic species, Line transects
National Category
Ecology
Identifiers
urn:nbn:se:su:diva-16101 (URN)10.1016/j.jmarsys.2008.03.028 (DOI)000262091600010 ()
Available from: 2008-12-13 Created: 2008-12-13 Last updated: 2017-12-13Bibliographically approved
2. Scale-dependent influence of environmental factors on species distribution: a case study on five benthic species in the Baltic Sea
Open this publication in new window or tab >>Scale-dependent influence of environmental factors on species distribution: a case study on five benthic species in the Baltic Sea
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Statistical modelling can be used to relate biological survey data to environmental factors, thereby providing a basis for predictive mapping of species or communities. However, there has been little discussion about the effect of scale on the predictive power of the variables used for species prediction. In this study, we analysed if the relative importance of environmental factors for the distribution of aquatic species was scale dependent, using data on the cover of five common benthic species (four macrophytes and one animal), from 1731 sites along the Swedish Baltic Sea coast. We modelled the cover and distribution of the five species in relation to salinity, depth, slope, wave exposure and substrate in scale steps from 25 to 1500 km, and analysed the relative contribution of the environmental variables to each species model. The average total deviance explained by the models was generally quite high, and decreased with increasing scale for all macrophyte species, while it increased for the animal, the Baltic Sea blue mussel, Mytilus edulis. The average contribution of salinity increased for all species when moving from local to Baltic Sea scale, and for the Baltic Sea blue mussel it was the single most important factor at the Baltic Sea scale. The average contribution of depth decreased with increasing scale for all species. However, regardless of scale, depth was the most important environmental factor to explain the distribution of all but one of the investigated macrophyte species. The relative contribution of different environmental variables changed with scale, and responses also differed between species. Factors measured on a fine scale, and thus describing local conditions were more influential at the local scale, whereas the large scale salinity gradient increased in importance with scale.

National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-54354 (URN)
Available from: 2011-01-31 Created: 2011-01-31 Last updated: 2011-01-31Bibliographically approved
3. Spatially dependent relationships between environmental factors and phytobenthic communities along the Swedish coast of the Baltic Sea, a numeric model approach
Open this publication in new window or tab >>Spatially dependent relationships between environmental factors and phytobenthic communities along the Swedish coast of the Baltic Sea, a numeric model approach
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The phytobenthic plant and animal communities are important components in the Baltic Sea ecosystem. In order to properly manage and monitor these communities the knowledge of structuring factors is important. In this study we used multivariate analyses to test the relative importance of environmental variables structuring the phytobenthic communities along the Swedish Baltic Sea coast, how the importance of these factors change with spatial scale and between the three main Baltic Sea sub-basins, the Baltic proper, Bothnian Sea and Bothnian Bay. We also studied the effect of these environmental factors for different species groups. The environmental factors included were salinity, wave exposure, substrate slope, depth and substrate type. For the analysis a large dataset of 1362 diving transects performed with comparable methods was used, describing the phytobenthic plant and animal species depth distribution and coverage. The environmental factors changed in importance at the different scales. The community-environment relationships also differed between the sub-basins, especially in the Bothnian Bay compared to the Baltic proper and Bothnian Sea. In the calculated best combination of factors correlating with the phytobenthic community the depth and the substrate were included in a majority of the analyses, both at different scales and in the different sub-basins. Differences in the correlation between the phytobenthic community and the environmental factors were also found between species groups. The differences between the spatial scales, the sub-basins and the species groups indicate that the criteria for environmental status, and stratification of sampling during local monitoring assessments, have to be area specific.

National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-54355 (URN)
Available from: 2011-01-31 Created: 2011-01-31 Last updated: 2011-01-31Bibliographically approved
4. Improvement of Baltic Sea coastal ecosystems indicated by increased distribution of Fucus vesiculosus L. since 1984
Open this publication in new window or tab >>Improvement of Baltic Sea coastal ecosystems indicated by increased distribution of Fucus vesiculosus L. since 1984
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Although there are several reports of continued eutrophication in the open Baltic Sea, we found increased distribution and depth penetration of Fucus vesiculosus in the coastal, phytobenthic system, indicating recovery. After a decline in depth penetration of Fucus in the Åland Sea by 3 m, from a maximum of 11.5 m in the 1940s to 8.5 m in 1984, the Fucus plants had again increased their depth distribution in 1992 and 1996, and in 2006 being back to the depths of the 1940s. Also, in the Askö area, data from the national monitoring programme show an increase of the Fucus maximum depth by 1 m between 1993 and 2009. We used Generalized Additive Models (GAM) to predict the change in percent cover of Fucus in the Askö area from 1993 to 2009. The largest change in Fucus coverage was predicted to occur in the inner parts of the archipelago, decreasing further out, thus being related to reductions in nutrient inputs from land sources. The field data however, showed the largest changes in the middle part since coverage and depth penetration of Fucus in the inner parts are limited by the quick change with depth from hard to soft substrates. In the Askö area the results in the inner archipelago could be linked to an increase in the spring Secchi depth since the beginning of the 1990s. The Secchi depth change was in accordance with the trends of decreasing spring primary production and chlorophyll-a concentration. As the most pronounced change in Secchi depth during the time period was a decrease in July and August, the summer conditions seem to have little influence on the depth distribution of Fucus.

Keyword
Eutrophication, Baltic Sea, Fucus vesiculosus, depth distribution, SCUBA, monitoring
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-54356 (URN)
Available from: 2011-01-31 Created: 2011-01-31 Last updated: 2011-01-31Bibliographically approved
5. Can long term changes of phytobenthic species be explained by climate or anthropogenic factors? A model approach based on monitoring data
Open this publication in new window or tab >>Can long term changes of phytobenthic species be explained by climate or anthropogenic factors? A model approach based on monitoring data
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In long term monitoring programmes it is important to distinguish between natural and anthropogenic changes. In the Baltic Sea, observed long term changes of the plant and animal communities have traditionally been explained by anthropogenic influence, while the natural fluctuations due to reoccurring climatic cycles was ignored. However, in recent years also the role of large scale climatic fluctuations for species distribution is discussed.

In this study four aquatic species with different life-history and distribution were modelled, using data from the years 1994 to 2007. The data were collected annually within the Swedish national monitoring programme of the northern Baltic proper. We analysed the occurrence of the annual or pseudoannual algae species Cladophora glomerata and Ceramium tenuicorne, the perennial algae Fucus vesiculosus and the phanerogame Potamogeton pectinatus to see if there was a temporal or spatial pattern that could be explained by climate or anthropogenic influence. The climate indices the North Atlantic Oscillation (NAO) and the Baltic Sea Index (BSI) was used as environmental variables in the analysis, together with water temperature, nutrient concentrations and chlorophyll-a content. As the effect of the climate variables might not show until the next growing season or later, the species distribution data were correlated to the environmental factors with a time-lag of 0 to 3 years. To find the large-scale variable that best explained the temporal variation of each species, Akaikes Information Criterion (AIC) was used to select the best model.

The annual alga Cladophora glomerata was best modelled by the concentration in the pelagic system of total nitrogen in April the same year. The correlation between Cladophora glomerata and total nitrogen was negative in areas where the predicted probability of species occurrence was high. The phanerogam Potamogeton pectinatus was best modelled by the temperature in November two years prior to sampling. The correlation between Potamogeton pectinatus and temperature in November two years prior to sampling was negative on sandy substrates, which was also where the predicted probability of species occurrence was high. For the pseudoannual alga Ceramium tenuicorne the variation in occurrence was best explained by the chlorophyll-a concentration in September two years prior to sampling, but the results were inconclusive. The inter-annual variation of the bladder-wrack Fucus vesiculosus was not well explained by any of the parameters chosen.

Our results indicated that on the time-scale of 15 years, single environmental variables are insufficient for explaining the spatial variability of phytobenthic species. The results also indicate that the phytobenthic system is roubust to the regular climatic variations as manifested in the NAO- and the BSI-cycles, since they only to a limited extent influence the species occurrence in the area.

National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-54357 (URN)
Available from: 2011-01-31 Created: 2011-01-31 Last updated: 2011-01-31Bibliographically approved

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