Aquatic insect community structure in urban ponds: effects of environmental variables Johan Andersson Degree project in biology, Master of science (2 years), 2014 Examensarbete i biologi 45 hp till masterexamen, 2014 Biology Education Centre and Department of Ecology and Genetics, Uppsala University Supervisor: Frank Johansson Table of Contents 1. ABSTRACT ..................................................................................................................................... 2 2. INTRODUCTION ........................................................................................................................... 2 3. METHODS ....................................................................................................................................... 4 3.1 STUDY SITES ................................................................................................................................................ 4 3.2 INSECT SAMPLING ...................................................................................................................................... 5 3.3 ENVIRONMENTAL VARIABLES .................................................................................................................. 6 3.4 VEGETATION COVER AND SHORELINE .................................................................................................... 6 3.5 CHEMICAL ANALYSIS OF WATER SAMPLES ............................................................................................ 7 3.6 LAND USE AND GIS ANALYSIS .................................................................................................................. 7 3.7 STATISTICAL ANALYSIS ............................................................................................................................. 8 4. RESULTS ......................................................................................................................................... 8 4.1 PRINCIPAL COMPONENTS ON ENVIRONMENTAL VARIABLES .............................................................. 8 4.2 INSECT RECORDS, ABUNDANCE AND DIVERSITY ................................................................................. 10 4.3 INSECT ASSEMBLAGES AND POND CHARACTERISTICS ....................................................................... 10 4.4 RICHNESS, ABUNDANCE AND DIVERSITY .............................................................................................. 12 5. DISCUSSION ................................................................................................................................ 13 5.1 THE EFFECT OF URBANIZATION ON AQUATIC INSECT COMMUNITY STRUCTURE .......................... 13 5.2 ENVIRONMENTAL EFFECTS ON SPECIES RICHNESS, ABUNDANCE AND DIVERSITY ....................... 14 5.3 SPECIES DETERMINATION – HIGHER TAXON APPROACH ................................................................... 15 5.4 NEWT PRESENCE ...................................................................................................................................... 16 5.5. SPECIES OF CONSERVATION CONCERN ................................................................................................ 16 5.6 FINAL CONCLUSION .................................................................................................................................. 16 6. ACKNOWLEDGEMENTS .......................................................................................................... 17 7. REFERENCES .............................................................................................................................. 17 8. APPENDICES ............................................................................................................................... 21 8.1 APPENDIX 1 – SPECIES LIST, OCCURRENCE AND FREQUENCY .......................................................... 21 8.2 APPENDIX 2 – INSECT ORDER SPECIFIC RDA BIPLOTS ..................................................................... 24 8.3 APPENDIX 3 – LAND USE DETAIL SPECIFICATIONS ............................................................................ 26 8.4 APPENDIX 4 – POND DESCRIPTIONS ..................................................................................................... 28 1 1. Abstract I sampled aquatic insects in 26 ponds of varying types in the urban landscape of the city of Stockholm and related insect community structure to environmental variables. I also related environmental factors to species richness, diversity and abundance of the sampled aquatic insects. A Redundancy Analysis (RDA) showed that the most important variables in explaining insect community structure was the remoteness to developed area and the amount of emergent vegetation in the ponds. Species richness increased with distance from developed area, diversity was related to floating vegetation and abundance of insects increased with distance from developed area and with higher amount of forestation and vegetation. The results of my study shows that urbanization effects divide the insect community into clusters of species that are tolerant or intolerant to effects of urbanisation. One internationally red-listed species, the dragonfly Leucorrhinia pectoralis was found in five (19,2%) of the ponds. My result suggested two important factors that should be considered when planning urban ponds. First, it is important to re-create varying types of ponds and include green buffer areas and second, plant colonisation should be facilitated to better mimic the natural states of ponds. 2. Introduction The urban landscape is continually expanding along with rising population levels. The proportion of people living in urban areas is forecasted to grow from 50% in 2008, to 69% globally in 2050 (United Nations Population Division 2011). In recent years the field of conservation biology has widened its trajectory from a view of preserving pristine ecosystems to also include areas highly influenced by human activities as important areas for nature and wildlife conservation (London Biodiversity Partnership 2001, Harrison & Davies 2002, Alvey 2006). Such areas could for example be green spaces within cities (Goddard et al. 2010), which is defined as an undeveloped open space at least partly covered with vegetation including community gardens, cemeteries and parks that often contain water (EPA 2013). Studies indicate that urbanization degrades biodiversity through various processes including e.g. habitat fragmentation (Dickman 1987), land conversion (Moore 1990) and introduction of alien species (Kowarik 2008). The future projections on extinction rates are depressive and the risk of more species becoming red-listed is increasing with urban development (McDonald et al. 2008). However it has also been shown that suburban areas contain a large biodiversity of organisms, often higher than the rural outskirts and the central urban areas. This is due to a broad variety of different habitats (McKinney 2008). For example, the common frog (Rana temporaria) in Great Britain has declined in rural areas, but has increased its abundance in urban areas (Carrier & Beebee 2003). Factors important for a stable population density of species in the urban landscape differ. For some species landscape barriers hinder migration and 2 dispersal (Blakely et al. 2006), whereas the major concern among other species is the habitat patch quality (Angold et al. 2006). These factors might be especially important in urban areas such as large cities because of the high fragmentation and the low habitat quality. Unfortunately they are not well studied in large cities and warrant more research focusing on the relationship between biodiversity and habitat quality in these areas. Even though ponds are not green in colour they are an important part of green spaces (Fontanarosa et al. 2013). The proportion of green-space associated with water can be quite large in cities (see refs in Gledhill et al. 2008). Traditionally ponds and smaller waters were filled in cities, but nowadays many ponds are often restored and new ones created (Gledhill & James 2012). These newly created ponds are used for urban drainage, nature conservation, ornament features and more (Sutherland & Hill 1995), and studies have suggested that ponds are important for human quality of life (Lees & Evans 2003). The biodiversity in ponds is affected by many abiotic and biotic factors. For example, it has been shown that size and connectedness of the ponds affect the species composition, with different species occurring in larger ponds than in a set of smaller ponds. Interestingly, a few smaller ponds can even harbour larger microfaunal diversity than one large pond (Oertli et al. 2002). Many life history traits of aquatic insects rely on interactions with plants. The relationships between species richness of insects and plants are quite well studied and some of the more important aspects of insect-plant interactions are: herbivory, oviposition, predator evasion and foraging (McGaha 1952). Numerous aquatic insects are susceptible to fish predation and presence of fish has been shown to play a key role in structuring aquatic insect communities (Bendell & McNicol 1987). Additionally the local water chemistry is affecting aquatic insect composition, where e.g. pH is a critical factor during the development of the larval stages with many species having problems coping with a too acidic environment (Bell 1971). Biodiversity in city ponds is also affected by land use/land-cover