| 1. |
- Andersson, Matilda L.
(författare)
-
Fish population responses to climate change : Causes and consequences
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lake environments are heterogeneous, and animals show a variety of adaptations to deal with this heterogeneity. Fish often show intraspecific variation in diet, metabolism, and behavior, corresponding to their habitat use. Studies on climate change often ignore this heterogeneity and its importance in determining population-level responses to climate change. This thesis can be broken into two interacting pieces. First, my goal was to assess how water color and temperature changes impact the size, number, and distribution of a common predator, Eurasian perch (Perca fluviatilis), in Swedish lakes. Second, I aimed to examine whether metabolism and resource use differed between lake habitats, corresponding with documented patterns of polymorphism and whether diet differences were maintained along a thermal and water color gradient. By combining the information gleaned from these studies, the overarching goal of my thesis is to better understand how climate change will impact fish populations and how intraspecific variance in these responses will impact ecosystem functioning. I found that warming and browning will likely decrease fish biomass but via different mechanisms. Warming reduces average fish size through its impact on metabolism and energy requirements. Browning decreases fish abundance likely due to its negative effects on resource abundance, increasing mortality, and decreasing reproductive effort. Though warming decreases biomass at the lake level, pelagic perch abundance increases. I found that these pelagic perch have higher metabolic rates and, especially in darker lakes, rely heavily on pelagic resources. As more fish shift into the pelagic habitat, this will increase top-down pressure on pelagic resources and decrease energy transfer from littoral to pelagic habitats altering energy flow within lakes. Variation in metabolic phenotype across habitats, combined with the positive scaling of metabolic rates with temperature, will likely determine which fish can persist under climate change scenarios. Studies that measure this variation rely heavily on respirometry to measure fish metabolism. I found that current respirometry methods underestimate maximum metabolic rate and suggest an updated method to improve the accuracy of future studies. Overall, I conclude that habitats should be examined separately to better understand population-level responses to climate change. Perch caught in different habitats have different energy requirements and respond differently to warming and browning. These differences will affect the distribution of top-down pressure and habitat coupling within lake ecosystems, with implications for broader ecosystem functioning in the future.
|
|
| 2. |
|
|
| 3. |
- Graco-Roza, Caio, et al.
(författare)
-
Distance decay 2.0 – A global synthesis of taxonomic and functional turnover in ecological communities
- 2022
-
Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 31:7, s. 1399-1421
-
Tidskriftsartikel (refereegranskat)abstract
- Aim: Understanding the variation in community composition and species abundances (i.e., beta-diversity) is at the heart of community ecology. A common approach to examine beta-diversity is to evaluate directional variation in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distance. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 148 datasets comprising different types of organisms and environments.Location: Global.Time period: 1990 to present.Major taxa studied: From diatoms to mammals.Method: We measured the strength of the decay using ranked Mantel tests (Mantel r) and the rate of distance decay as the slope of an exponential fit using generalized linear models. We used null models to test whether functional similarity decays faster or slower than expected given the taxonomic decay along the spatial and environmental distance. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm and organismal features.Results: Taxonomic distance decay was stronger than functional distance decay along both spatial and environmental distance. Functional distance decay was random given the taxonomic distance decay. The rate of taxonomic and functional spatial distance decay was fastest in the datasets from mid-latitudes. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distance but a higher rate of decay along environmental distance. Marine ecosystems had the slowest rate of decay along environmental distances.Main conclusions: In general, taxonomic distance decay is a useful tool for biogeographical research because it reflects dispersal-related factors in addition to species responses to climatic and environmental variables. Moreover, functional distance decay might be a cost-effective option for investigating community changes in heterogeneous environments.
|
|
| 4. |
- Hampton, Stephanie E., et al.
(författare)
-
Ecology under lake ice
- 2017
-
Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 20:1, s. 98-111
-
Forskningsöversikt (refereegranskat)abstract
- Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.
|
|
| 5. |
|
|
| 6. |
- Hayden, Brian T., et al.
(författare)
-
Single or Double Degenerate Progenitors? Searching for Shock Emission in the SDSS-II Type Ia Supernovae
- 2010
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 722:2, s. 1691-1698
-
Tidskriftsartikel (refereegranskat)abstract
- From the set of nearly 500 spectroscopically confirmed Type Ia supernovae (SNe) and around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108 confirmed SNe Ia with well-observed early-time light curves to search for signatures from shock interaction of the SN with a companion star. No evidence for shock emission is seen; however, the cadence and photometric noise could hide a weak shock signal. We simulate shocked light curves using SN Ia templates and a simple Gaussian shock model to emulate the noise properties of the SDSS-II sample and estimate the detectability of the shock interaction signal as a function of shock amplitude, shock width, and shock fraction. We find no direct evidence for shock interaction in the rest-frame B-band, but place an upper limit on the shock amplitude at 9% of SN peak flux (MB > - 16.6 mag). If the single degenerate channel dominates type Ia progenitors, this result constrains the companion stars to be less than about 6 M sun on the main sequence and strongly disfavors red giant companions.
|
|
| 7. |
- Hayden, Brian T., et al.
(författare)
-
The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II Supernova Survey
- 2010
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 712:1, s. 350-366
-
Tidskriftsartikel (refereegranskat)abstract
- We analyze the rise and fall times of Type Ia supernova (SN Ia) light curves discovered by the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. From a set of 391 light curves k-corrected to the rest-frame B and V bands, we find a smaller dispersion in the rising portion of the light curve compared to the decline. This is in qualitative agreement with computer models which predict that variations in radioactive nickel yield have less impact on the rise than on the spread of the decline rates. The differences we find in the rise and fall properties suggest that a single "stretch" correction to the light curve phase does not properly model the range of SN Ia light curve shapes. We select a subset of 105 light curves well observed in both rise and fall portions of the light curves and develop a "2-stretch" fit algorithm which estimates the rise and fall times independently. We find the average time from explosion to B-band peak brightness is 17.38 ± 0.17 days, but with a spread of rise times which range from 13 days to 23 days. Our average rise time is shorter than the 19.5 days found in previous studies; this reflects both the different light curve template used and the application of the 2-stretch algorithm. The SDSS-II supernova set and the local SNe Ia with well-observed early light curves show no significant differences in their average rise-time properties. We find that slow-declining events tend to have fast rise times, but that the distribution of rise minus fall time is broad and single peaked. This distribution is in contrast to the bimodality in this parameter that was first suggested by Strovink from an analysis of a small set of local SNe Ia. We divide the SDSS-II sample in half based on the rise minus fall value, tr - tf <= 2 days and tr - tf > 2 days, to search for differences in their host galaxy properties and Hubble residuals; we find no difference in host galaxy properties or Hubble residuals in our sample.
|
|
| 8. |
- Hayden, Brian, et al.
(författare)
-
The HST See Change Program. I. Survey Design, Pipeline, and Supernova Discoveries
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 912:2
-
Tidskriftsartikel (refereegranskat)abstract
- The See Change survey was designed to make z > 1 cosmological measurements by efficiently discovering high-redshift Type Ia supernovae (SNe Ia) and improving cluster mass measurements through weak lensing. This survey observed twelve galaxy clusters with the Hubble Space Telescope (HST) spanning the redshift range z = 1.13-1.75, discovering 57 likely transients and 27 likely SNe Ia at z similar to 0.8-2.3. As in similar previous surveys, this proved to be a highly efficient use of HST for supernova observations; the See Change survey additionally tested the feasibility of maintaining, or further increasing, the efficiency at yet higher redshifts, where we have less detailed information on the expected cluster masses and star formation rates. We find that the resulting number of SNe Ia per orbit is a factor of similar to 8 higher than for a field search, and 45% of our orbits contained an active SN Ia within 22 rest-frame days of peak, with one of the clusters by itself yielding 6 of the SNe Ia. We present the survey design, pipeline, and supernova discoveries. Novel features include fully blinded supernova searches, the first random forest candidate classifier for undersampled IR data (with a 50% detection threshold within 0.05 mag of human searchers), real-time forward-modeling photometry of candidates, and semi-automated photometric classifications and follow-up forecasts. We also describe the spectroscopic follow-up, instrumental in measuring host galaxy redshifts. The cosmology analysis of our sample will be presented in a companion paper.
|
|
| 9. |
|
|
| 10. |
- Lau, Danny C. P., et al.
(författare)
-
Multitrophic biodiversity patterns and environmental descriptors of sub‐Arctic lakes in northern Europe
- 2022
-
Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 67:1, s. 30-48
-
Tidskriftsartikel (refereegranskat)abstract
- 1. Arctic and sub‐Arctic lakes in northern Europe are increasingly threatened by climate change, which can affect their biodiversity directly by shifting thermal and hydrological regimes, and indirectly by altering landscape processes and catchment vegetation. Most previous studies of northern lake biodiversity responses to environmental changes have focused on only a single organismal group. Investigations at whole‐lake scales that integrate different habitats and trophic levels are currently rare, but highly necessary for future lake monitoring and management.2. We analysed spatial biodiversity patterns of 74 sub‐Arctic lakes in Norway, Sweden, Finland, and the Faroe Islands with monitoring data for at least three biological focal ecosystem components (FECs)—benthic diatoms, macrophytes, phytoplankton, littoral benthic macroinvertebrates, zooplankton, and fish—that covered both pelagic and benthic habitats and multiple trophic levels.3. We calculated the richnessrelative (i.e. taxon richness of a FEC in the lake divided by the total richness of that FEC in all 74 lakes) and the biodiversity metrics (i.e. taxon richness, inverse Simpson index (diversity), and taxon evenness) of individual FECs using presence–absence and abundance data, respectively. We then investigated whether the FEC richnessrelative and biodiversity metrics were correlated with lake abiotic and geospatial variables. We hypothesised that (1) individual FECs would be more diverse in a warmer and wetter climate (e.g. at lower latitudes and/or elevations), and in hydrobasins with greater forest cover that could enhance the supply of terrestrial organic matter and nutrients that stimulated lake productivity; and (2) patterns in FEC responses would be coupled among trophic levels.4. Results from redundancy analyses showed that the richnessrelative of phytoplankton, macrophytes, and fish decreased, but those of the intermediate trophic levels (i.e. macroinvertebrates and zooplankton) increased with decreasing latitude and/or elevation. Fish richnessrelative and diversity increased with increasing temporal variation in climate (temperature and/or precipitation), ambient nutrient concentrations (e.g. total nitrogen) in lakes, and woody vegetation (e.g. taiga forest) cover in hydrobasins, whereas taxon richness of macroinvertebrates and zooplankton decreased with increasing temporal variation in climate.5. The similar patterns detected for richnessrelative of fish, macrophytes, and phytoplankton could be caused by similar responses to the environmental descriptors, and/or the beneficial effects of macrophytes as habitat structure. By creating habitat, macrophytes may increase fish diversity and production, which in turn may promote higher densities and probably more diverse assemblages of phytoplankton through trophic cascades. Lakes with greater fish richnessrelative tended to have greater average richnessrelative among FECs, suggesting that fish are a potential indicator for overall lake biodiversity.6. Overall, the biodiversity patterns observed along the environmental gradients were trophic‐level specific, indicating that an integrated food‐web perspective may lead to a more holistic understanding of ecosystem biodiversity in future monitoring and management of high‐latitude lakes. In future, monitoring should also focus on collecting more abundance data for fish and lower trophic levels in both benthic and pelagic habitats. This may require more concentrated sampling effort on fewer lakes at smaller spatial scales, while continuing to sample lakes distributed along environmental gradients.
|
|
