Metapopulation ecology of Notonecta in small ponds Robert Andrew Briers Submitted for the degree of Doctor of Philosophy Department of Animal and Plant Sciences University of Sheffield November 1998 Metapopulation ecology of Notonecta in small ponds. Robert Andrew Briers Abstract. This thesis considers the application of metapopulation theory to a field system; two species of Notonecta (Hemiptera: Heteroptera, Notonectidae), a freshwater invertebrate predator, inhabiting a series of small man-made ponds known as dewponds, in the Peak District, Derbyshire. Surveys of pond occupancy and habitat characteristics examined the habitat preferences and spatial population dynamics of the two species, and associations between Notonecta and other taxa. Interspecific competition and predation between nymphs were investigated in the laboratory and in field mesocosms to determine their potential influence on field distributions. The two species have contrasting habitat preferences, and breed in a subset of all ponds in the area. Choice of oviposition substrate appears to be an important mechanism of habitat selection. The landscape scale population dynamics of Notonecta resemble those predicted by metapopulation models, but regional persistence is determined by the availability and distribution of suitable habitat across the landscape, rather than by a dynamic balance of stochastic colonisation and extinction. Where the species co-occur, competition is likely and the outcome is influenced by the amount of submerged vegetation present, which affects the feeding efficiency of the two species. Associations between Notonecta and other taxa largely appear to result from covariance in response to habitat factors; the distributions of Notonecta and potential prey do not seem to be strongly linked. Most metapopulation models assume that habitat is static, but in common with many other field systems, metapopulation dynamics of Notonecta appear to be driven by dynamic changes in habitat of individual patches. This suggests that in order to be of greater practical value, future developments in metapopulation theory must incorporate effects of habitat dynamics on regional persistence and distribution. Acknowledgements. I would like to thank Phil Warren for his patient, supportive and always constructive supervision throughout the course of this work. Many thanks are also due to my wife, Kerrera, who tolerated the intrusion of research into 'normal' life, provided constant support and encouragement, and even came out to the dewponds in the snow. I am grateful to my parents, who actively encouraged my exploration of all things wet and wonderful. Anita Weatherby, John Brewington and Matt Spencer are thanked for providing a stimulating atmosphere in which to work and think. Allison Blake helped smooth the path in the lab and John Shutt provided assistance with diverse technical requirements. I have greatly benefited from discussion of various aspects of this work with John Boothby, John Bowker, Kevin Gaston, Paul Giller, Volker Grimm, Mike Jeffries, Lorraine Maltby, John Spicer and Don Whittle, and correspondence with Alan Savage and F.A. Streams. Steve Wise from SCGISA provided GIS advice and Rhodri Thomas from the Peak National Park Authority gave access to unpublished survey work and maps of dewpond locations. Finally I would like to thank all the farmers and landowners who generously granted me access to the dewponds on their land, and provided valuable background information about the ponds. Contents. 1. Introduction .......................................................................................................... 1 1.1 General introduction ....................................................................................... 1 l.2 Metapopulations and metapopulation theory ................................................... 2 1.3 Dewponds ...................................................................................................... 6 l.4 Biology of Notonecta ..................................................................................... 11 1.5 Overview of this study ................................................................................... 16 2. General methodology and biological background ................................................ 18 2.1 Introduction ................................................................................................... 18 2.2 Laboratory rearing of Notonecta .................................................................... 18 2.3 Nymph identification ...................................................................................... 19 2.4 Age:head width relationships .......................................................................... 20 2.5 Field sampling techniques ............................................................................... 20 2.6 Habitat survey and dewpond characteristics .................................................... 22 2.7 Seasonal population dynamics ........................................................................ 23 3. Habitat preferences .............................................................................................. 24 3.1 Introduction ................................................................................................... 24 3.2 Habitat characteristics .................................................................................... 27 3.2.1 Methods ............................................................................................... 27 3.2.2 Results ................................................................................................. 29 3.2.3 Discussion ............................................................................................ 33 3.3 Incidence functions ......................................................................................... 37 3.3.1 Methods ............................................................................................... 37 3.3.2 Results ................................................................................................. 38 3.3.3 Discussion ............................................................................................ 41 3.4 Oviposition preferences .................................................................................. 44 3.4.1 Methods ............................................................................................... 44 3.4.2 Results ................................................................................................. 45 3.4.3 Discussion ............................................................................................ 45 3.5 Conclusions ................................................................................................... 41 4. Spatial popUlation dynamics ................................................................................. 49 4.1 Introduction ................................................................................................... 49 4.2 Occupancy dynamics and population turnover ................................................ 51 4.2.1 Introduction .......................................................................................... 51 4.2.2 Changes in regional occupancy .............................................................. 51 4.2.3 Population turnover .............................................................................. 53 4.2.4 Discussion ............................................................................................ 54 4.3 Colonisation and dispersal .............................................................................. 58 4.3.1 Introduction .......................................................................................... 58 4.3.2 Methods ............................................................................................... 59 4.3.3 Results ................................................................................................. 62 4.3.4 Discussion ............................................................................................ 64 4.4 Local extinction ............................................................................................. 67 4.4.1 Introduction .......................................................................................... 67 4.4.2 Methods ............................................................................................... 69 4.4.3 Results ................................................................................................. 71 4.4.4 Discussion ............................................................................................ 74 4.5 Conclusions ................................................................................................... 80 5. Competition and coexistence ................................................................................ 81 5.1 General introduction ....................................................................................... 81 5.2 Competition between nymphs ......................................................................... 83 5.2.1 Summary .............................................................................................. 85 5.2.2 Introduction .......................................................................................... 86 5.2.3 Study system ........................................................................................ 87 5.2.4 Materials and methods .........................................................................