<p>Although there is much theoretical and empirical data about the life history responses of time constrained organisms, little is known about the latitude compensating mechanism that enables northern populations’ developmental rates to compensate for latitude. To investigate the importance of photoperiod on development and growth, I collected adults and raised the offspring of the obligatory univoltine damselfly Lestes sponsa from two populations at different latitudes (53º N and 63º N). The offspring were raised in a common laboratory environment at 21º C and at the two photoperiods corresponding to the sites of collection. Field data showed that adult and egg sizes decreased towards the higher latitude. This adult size difference was a genetically fixed trait since the same size difference between populations was also found when larvae where reared in the laboratory. All studied individuals expressed shorter development time and faster growth rates under northern photoperiod regimes. Northern damselflies showed fixed body size and mass at emergence despite being reared at different photoperiod conditions. Similarly, southern individuals kept body size at emergence constant at both photoregimes, but overcompensated shorter development time in the northern photoregime by gaining higher body mass than in original,southern photoregime. There was no difference in hatching synchronisation between larvae from the south and the north. I found evidence of higher synchrony at adult emergence among northern individuals. The previous investigation of L. sponsa phenology in natural conditions together with these laboratory results indicate the presence of the latitude compensating mechanism that is triggered by a response to photoperiod. A positive correlation between photoperiod and developmental rate in this damselfly, and probably in many other temperate insect species, might be adaptive since it optimises the life history stage transitions and body size/mass at each latitude.</p>

Es gibt bereits viele Hinweise dafür, dass Seen sehr sensibel auf die anthropogen verursachte Klimaerwärmung reagiert haben. Bis jetzt haben sich die Studien der Klimafolgenforschung hauptsächlichst auf die Auswirkungen der Erwärmung im Winter und Frühling konzentriert. Über den Einfluss der Klimaerwärmung auf Seen in den gemäßigten Breiten im Sommer ist weniger bekannt. In der vorliegenden Doktorarbeit habe ich einige Faktoren, welche die Reaktion von Seen auf die Erwärmung im Sommer vermutlich stark mitbestimmt haben, untersucht. Der Schwerpunkt lag dabei auf klimatisch induzierten Auswirkungen auf die thermische Charakteristik und die Phänologie und Abundanz des Planktons eines flachen und polymiktischen Sees (Müggelsee, Berlin). Zuerst wurde der Einfluss der Klimaerwärmung auf die Phänologie und Abundanz des Planktons in verschiedenen Jahreszeiten untersucht. Das schnellwachsende Phyto- und Zooplankton (Daphnia) im Frühjahr hat sich vorwiegend synchron vorverschoben, wohingegen Veränderungen des Sommerzooplanktons deutlich artspezifisch und nicht synchron waren. Die Phänologie oder Abundanz einiger Sommercopepoden hat sich entsprechend der individuellen thermischen Anforderungen innerhalb bestimmter Entwicklungsstufen, wie zum Beispiel der Emergenz von der Diapause im Frühling, verändert. Die Studie unterstreicht, dass nicht nur der Grad der Erwärmung, sondern auch dessen Zeitpunkt innerhalb des Jahres von großer ökologischer Bedeutung ist. Um die Auswirkungen des Klimawandels auf die thermischen Eigenschaften des Sees zu erforschen, habe ich die Langzeitentwicklung der täglichen epilimnischen Temperaturextrema während des Sommers untersucht. Durch diese Studie wurde zum ersten Mal für Seen gezeigt, dass die täglichen epilimnischen Minima (Nacht) stärker angestiegen sind als die Maxima (Tag), wodurch sich der tägliche epilimnische Temperaturbereich deutlich verringert hat. Diese Tag-Nacht-Asymmetrie in der epilimnischen Temperatur wurde durch eine erhöhte Emission von Langwellenstrahlung aus der Atmosphäre während der Nacht verursacht. Dies unterstreicht, dass nicht nur Erhöhungen der Lufttemperatur, sondern auch Änderungen anderer meteorologischer Variablen wie der Windgeschwindigkeit, der Luftfeuchte und der Bewölkung eine wichtige Rolle bei der Bestimmung der Seetemperatur im Hinblick auf weitere Klimaveränderungen spielen werden. Zudem wurde eine Kurzzeitanalyse zum Schichtungsverhalten des polymiktischen Sees durchgeführt, um die Häufigkeit und Dauer von Schichtungsereignissen und deren Einfluss auf den gelösten Sauerstoff, die gelösten Nährstoffe und das Phytoplankton zu untersuchen. Selbst während der längsten Schichtungsereignisse (Hitzewellen 2003 und 2006) unterschieden sich die Auswirkungen auf den See von denen, welche in flachen dimiktischen Seen während der kontinuierlichen Sommerschichtung auftreten. Die hypolimnische Temperatur war höher, was die Sauerstoffzehrung und die Akkumulation von gelösten Nährstoffen begünstigt hat. Die thermische Schichtung wird in Zukunft sehr wahrscheinlich zunehmen. Dies lässt darauf schließen, dass polymiktische Seen sehr anfällig gegenüber Änderungen im Hinblick auf projizierte Klimaveränderungen sein werden. Abschließend wurde eine Studie über Lang- und Kurzzeitveränderungen in der Entwicklung der planktischen Larven der Muschel Dreissena polymorpha durchgeführt, um den Einfluss der Veränderungen im thermischen und trophischen Regime des Sees zu analysieren. Die Klimaerwärmung und die Verringerung in der externen Nährstofffracht haben die Abundanz der Larven stark beeinflusst indem sie jeweils auf bestimmte Entwicklungsphasen dieser Art während der warmen Jahreszeiten gewirkt haben. Der Anstieg in der Abundanz und der Länge der Larven stand im Zusammenhang mit dem Rückgang der Nährstofffracht und der Veränderung der Phytoplanktonzusammensetzung. Die Hitzewellen in den Jahren 2003 und 2006 haben diesen positiven Effekt auf die Larvenabundanz jedoch durch ungünstige Sauerstoffkonzentrationen während der sehr langen Schichtung aufgehoben. Die Klimaerwärmung kann demzufolge entgegenwirkende Effekte in produktiven flachen Seen, in welchen die externe Nährstofffracht reduziert wurde, auslösen. Aus diesen Ergebnissen schließe ich, dass nicht nur die Art des Klimawandels und damit der Zeitpunkt der Erwärmung und das Auftreten von Extremen wie Hitzewellen, sondern auch standortspezifische Bedingungen wie Schichtungsverhalten und Trophiegrad entscheidende Faktoren sind, welche die Auswirkungen der Klimaerwärmung auf interne Seeprozesse im Sommer bestimmen. Somit sollte sich die weiterführende Klimafolgenforschung für Seen darauf konzentrieren, wie verschiedene Seetypen auf die komplexen Umweltveränderungen im Sommer reagieren, damit ein umfassenderes Verständnis über den Einfluss von anthropogen verursachten Veränderungen auf Seen der gemäßigten Breiten erreicht wird. / There is already strong evidence that temperate lakes have been highly vulnerable to human induced climate warming during the last century. Hitherto climate impact studies have mainly focussed on the impacts of the recent long-term warming in winter and spring and little is known on the influence of climate warming on temperate lakes in summer. In the present thesis, I studied some aspects, which may have been strongly involved in determining the response of a lake to climate warming in summer. Thereby I have focussed on climate induced impacts on the thermal characteristics and the phenology and abundance of summer plankton in a shallow polymictic lake (Müggelsee, Germany). First, the influence of climate warming on the phenology and abundance of the lake plankton was investigated across seasons. Fast-growing spring phytoplankton and zooplankton (Daphnia) advanced largely synchronously, whereas long-term changes in the phenology of slow-growing summer zooplankton were clearly species-specific and not synchronised. The phenology and/or abundance of several summer copepod species changed according to their individual thermal requirements at decisive developmental stages such as emergence from diapause in spring. The study emphasises that not only the degree of warming, but also its timing within the annual cycle is of great ecological importance. To analyse the impact of climate change on the thermal characteristics of the lake, I examined the long-term development of the daily epilimnetic temperature extrema during summer. The study demonstrated for the first time for lakes that the daily epilimnetic minima (during nighttime) have increased more rapidly than the daily epilimnetic maxima (during daytime), resulting in a distinct decrease in the daily epilimnetic temperature range. This day-night asymmetry in epilimnetic temperature was likely caused by an increased nighttime emission of long-wave radiation from the atmosphere. This underlines that not only increases in air temperature, but also changes in other meteorological variables such as wind speed, relative humidity and cloud cover may play an important role in determining the lake temperature with respect to further climate change. Furthermore, a short-term analysis on the mixing regime of the polymictic lake was conducted to examine the frequency and duration of stratification events and their impacts on dissolved oxygen, dissolved nutrients and summer phytoplankton. Even during the longest stratification events (heatwaves in 2003 and 2006) the thermal characteristics of the lake differed from those typically found in shallow dimictic lakes, which exhibit a continuous stratification during summer. Particularly, hypolimnetic temperatures were higher, favouring the depletion of oxygen and the accumulation of dissolved nutrient in the hypolimnion. Thermal stratification will be very likely amplified in the future, thus, I conclude that polymictic lakes will be very vulnerable to alterations in the thermal regime with respect to projections of further climate change during summer. Finally, a long-term case study on the long and short-term changes in the development of the planktonic larvae of the freshwater mussel Dreissena polymorpha was performed to analyse the impacts of simultaneous changes in the thermal and in the trophic regime of the lake. Both the climate warming and the decrease in external nutrient load were important in determining the abundance of the pelagic larvae by affecting different features of the life-history of this species throughout the warm season. The long-term increase in the abundance and length of larvae was related to the decrease in external nutrient loading and the change in phytoplankton composition. However, the recent heatwaves in 2003 and 2006 have offset this positive effect on larval abundance, due to unfavourable low oxygen concentrations that had resulted from extremely long stratification events, mimicking the effects of nutrient enrichment. Climate warming may thus induce counteracting effects in productive shallow lakes that underwent lake restoration through a decrease in external nutrient loading. I conclude that not only the nature of climate change and thus the timing of climate warming throughout the seasons and the occurrence of climatic extremes as heatwaves, but also site-specific lake conditions as the thermal mixing regime and the trophic state are crucial factors governing the impacts of climate warming on internal lake processes during summer. Consequently, further climate impact research on lake functioning should focus on how the different lake types respond to the complex environmental forcing in summer, to allow for a comprehensive understanding of human induced environmental changes in lakes.

In the spring of 2007 the Kuba Dam in Nätra Stream was removed for restoration purposes, mainly to give free passage to migrating fish. This action gave an opportunity to study the effects of dam removal on organisms both on land and in water, a type of study which is in demand for planning purposes of future dam removals. This study focuses on the effects upon the vegetation along the stream where the former reservoir was situated. Willow cuttings and sunflower seeds were used as phytometers to assess the growth conditions one year after removal at three different elevation levels at four different sites along the Nätra Stream. The reaches studied were the former reservoir of Kuba Dam (Site A), the area just downstream of this former dam (Site B), further upstream in the reservoir of the existing Nyfors Dam (Site C), and even further upstream at Myreforsen, a reference area not affected by dams (Site D). Willow cuttings and sunflower seeds were planted at three different riparian levels at the sites in June and left to grow until August when growth results were collected. Many of the cuttings had died but statistically significant differences between sites could still be detected. They showed that the former reservoir shorelines in Kuba (Site A) had a plant growth significantly higher than the other regulated site. In other words, it was no longer equal to an existing reservoir but not yet similar to a free-flowing reach. The western side of the stream at this site had a higher growth than the eastern side and also higher than all the other sites. As for the three levels, the results showed a higher growth at the lowest elevation level at site A than all at the other levels and sites. This suggests that a combination of good access to sunlight and nutrients and fine-grade moist substrate results in a good growing conditions nearer the water in this former reservoir. The results for the sunflower seeds showed that the reference reach had a higher colonization success than the other sites. / Utrivningen av Kubadammen i Nätraån våren 2007 gav möjlighet att studera och följa upp hur en sådan förändring påverkar organismer på land och i vatten både uppströms och nedströms den tidigare dammen. Denna typ av undersökningar efterfrågas allt mer i och med att fler och fler dammar rivs av olika anledningar. I Kubadammens fall hade dammen förlorat sin ursprungliga roll och de fördelar som magasinet förde med sig för bland annat rekreation vägde inte längre upp dämningens negativa effekter på vattendragets ekosystem, till exempel som vandringshinder för fiskar. I denna studie har fokus lagts på vad som sker med vegetationen på stränderna längs det forna vattenmagasinet efter rivning. Med hjälp av videkvistar och solrosfrön som fytometrar undersöktes tillväxten ett år efter rivning på tre olika strandnivåer på fyra olika lokaler längs Nätraån. Dessa lokaler var Kubadammens gamla magasin (Lokal A), området direkt nedströms den före detta dammen (Lokal B), den nuvarande Nyforsdammens magasin (Lokal C) uppströms den före detta dammen, samt en referenssträcka vid Myreforsen (Lokal D) uppströms alla Nätraåns dammar och därmed ej påverkad av dämningseffekter. Videkvistarna och solrosorna planterades på tre nivåer på de olika lokalerna i juni och tilläts växa till augusti då tillväxtresultaten samlades in. Många kvistar hade dött under tiden men tillräckligt många överlevde för att det skulle gå att läsa ut statistiskt signifikanta skillnader i tillväxt. Resultaten visade att det före detta magasinet vid Kuba (Lokal A) hade en signifikant högre tillväxt än de andra lokalerna, vilket visar på att tillväxtförhållandena för vide varken liknar dem i ett befintligt magasin eller på en orörd sträcka eller nedströmssträckan, utan var betydligt mer gynnsamma. På denna lokal växte fytometrarna dessutom signifikant bättre på den västra sidan än på den östra sidan. När man ser till de tre nivåerna så växte videkvistarna i nivån närmast vattnet i det före detta magasinet vid Kuba bättre än på de övriga nivåerna på samma lokal och på de övriga lokalerna. Troligtvis beror detta på en kombination av öppenhet som ger bra tillgång till solljus, bra näringstillgång, substratets finkornighet och förmåga att hålla kvar fukt närmare vattnet. Resultaten av solrosfrönas etablering visade på att referenssträckan hade en högre etablering än övriga lokaler.

Although there is much theoretical and empirical data about the life history responses of time constrained organisms, little is known about the latitude compensating mechanism that enables northern populations’ developmental rates to compensate for latitude. To investigate the importance of photoperiod on development and growth, I collected adults and raised the offspring of the obligatory univoltine damselfly Lestes sponsa from two populations at different latitudes (53º N and 63º N). The offspring were raised in a common laboratory environment at 21º C and at the two photoperiods corresponding to the sites of collection. Field data showed that adult and egg sizes decreased towards the higher latitude. This adult size difference was a genetically fixed trait since the same size difference between populations was also found when larvae where reared in the laboratory. All studied individuals expressed shorter development time and faster growth rates under northern photoperiod regimes. Northern damselflies showed fixed body size and mass at emergence despite being reared at different photoperiod conditions. Similarly, southern individuals kept body size at emergence constant at both photoregimes, but overcompensated shorter development time in the northern photoregime by gaining higher body mass than in original,southern photoregime. There was no difference in hatching synchronisation between larvae from the south and the north. I found evidence of higher synchrony at adult emergence among northern individuals. The previous investigation of L. sponsa phenology in natural conditions together with these laboratory results indicate the presence of the latitude compensating mechanism that is triggered by a response to photoperiod. A positive correlation between photoperiod and developmental rate in this damselfly, and probably in many other temperate insect species, might be adaptive since it optimises the life history stage transitions and body size/mass at each latitude.

No description available.

No description available.

Sötvattensmusslor har en viktig roll i akvatiska ekosystem och de anses vara en av de mest sårbara och hotade organismgrupperna i sötvatten. Sverige har nio arter stormusslor, varav fyra är upptagna på den svenska rödlistan. Flest studier har gjorts på flodpärlmusslor (Margaritifera margaritifera) och hoten som den står inför. Undersökningar av de vanligare förekommande arterna i Västra Götalands län, har visat att även allmän dammussla (Anodonta anatina) och spetsig målarmussla (Unio tumidus) har problem med livskraftiga bestånd och föryngring. Stormusslor anses vara som mest sårbara när de som juvenila ligger nedgrävda i sedimenten. Den här studien har mätt kvaliteten av sedimenten i tolv mussellokaler i Västra Götalands län. Mätningar har gjorts av den centralt viktiga variabeln redoxpotentialen, för att se om den kan vara kopplad till den dåliga föryngringen. Även sammansättningen av vattendragens kantzoner inom mussellokalernas delavrinningsområden har studerats, då de är nära länkade till ekosystemen i sedimenten och även har en fundamental roll för hur vattendragens ekosystem fungerar. Analyser med hjälp av regressionsträd visade att den variabel med störst påverkan på musslornas täthet, var differensen i redoxpotentialer mellan 0 cm och 5 cm djup. Störst påverkan på föryngringen hade andelen sjöareal i delavrinningsområdet. Ett icke-parametriskt test som utfördes visade att andelen myrmark i kantzonen var positivt korrelerad till föryngringen av allmän dammussla (A. anatina). Andelen ungskog i kantzonen var negativt korrelerad till föryngringen av spetsig målarmussla (U. tumidus). Mer omfattande mätningar av redoxpotentialer än som varit möjliga i den här studien, skulle kunna ge värdefull kunskap om hur situationen verkligen förhåller sig i de juvenilas habitat. Vidare studier av stormusslornas populationer skulle underlätta bedömningen om livskraftiga bestånd. / Freshwater mussels, who have a central role in aquatic ecosystems, are considered one of the most vulnerable and threatened freshwater organism groups. Sweden has nine species of large freshwater mussels, which of four are listed in the national Red List. Most studies and research have been focused on the freshwater pearl mussel (Margaritifera margaritifera) and its possible threats. Studies of more common species like the duck mussel (Anodonta anatina) and swollen river mussel (Unio tumidus) in Västra Götaland district, indicates severe difficulties of recruitment and viable populations. The most vulnerable phase in the life of freshwater mussels is considered to be the juvenile phase, when they are embedded in the sediment. The aim of this study has been to measure the quality of sediments at 12 of the earlier studied sites in Västra Götaland district. Redox potentials, which is a master variable in aquatic ecosystems and control parts of the chemistry in sediments, have been measured to analyze a possible correlation to the poor recruitment. The structure of the riparian buffer zones of the mussel’s unique catchment areas, have also been analyzed. The buffer zones are closely linked to the sediment ecosystems and have a fundamental role in the function of the ecosystems of streams. Analysis of regression trees indicated the most impacting factor on the mussel density, to be the difference of the mean redox value between the sediment surface and the depth of five centimeters. The variable with most impact on the recruitment was the proportion of area between catchment and lake. A none-parametric test showed a positive correlation between the proportion of marshes in the riparian buffer zone and the recruitment of A. anatina. A negative correlation existed between the proportion of young forests in the buffer zone and the recruitment of U. tumidus. More extended studies of redox potentials than was possible in this thesis, could contribute with valuable information of the quality of juvenile habitat. Further studies of the freshwater mussels could facilitate the evaluation of viable populations.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 117-125.

No description available.

The consequences of introducing riparian shade on in-stream community structure has not been well explored in south-eastern Australia. With catchment managers focusing on revegetation of riparian zones, there is a need to understand, monitor, and predict changes in ecological patters and processes that may take place as a system shifts from an open to a shaded stream community. Presented in this thesis is a conceptual model portraying possible responses of a macrophyte community to light reduction as a result of the introduction of riparian vegetation. This model was tested in the field by artificially shading sites (three shade treatments) to observe the direct effects of light reduction on Phragmites australis growth and structure and flow-on effects to associated in-stream biota." / Doctor of Philosphy