| 1. |
- Brodersen, Jakob, et al.
(författare)
-
Condition-dependent individual decision-making determines cyprinid partial migration
- 2008
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 89:5, s. 1195-1200
-
Tidskriftsartikel (refereegranskat)abstract
- Partial migration is a common phenomenon among many animals and occurs in many types of ecosystems. Understanding the mechanisms behind partial migration is of major importance for the understanding of population dynamics and, eventually, ecosystem processes. We studied the effects of food availability on the seasonal partial migration of cyprinid fish from a lake to connected streams during winter by the use of passive telemetry. Fish with increased access to food were found to migrate in higher proportion, earlier in the season, and to reside in the streams for a longer period compared to fish with decreased access to food. Furthermore, fewer unfed migrants returned to the lake, indicating higher overwinter mortality. Our results suggest that individual fish trade off safety from predation and access to food differently depending on their body condition, which results in a condition-dependent partial migration. Hence, our main conclusion is that individual decision-making is based on assessment of own condition which offers a mechanistic explanation to partial migration. Moreover, this may be of high importance for understanding population responses to environmental variation as well as ecosystem dynamics and stability. Read More: http://www.esajournals.org/doi/abs/10.1890/07-1318.1
|
|
| 2. |
- Hansson, Lars-Anders, et al.
(författare)
-
Escape from UV threats in zooplankton: A cocktail of behavior and protective pigmentation
- 2007
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 88:8, s. 1932-1939
-
Tidskriftsartikel (refereegranskat)abstract
- In order to avoid environmental threats, organisms may respond by altering behavior or phenotype. Using experiments performed in high-latitude Siberia and in temperate Sweden, we show for the first time that, among freshwater crustacean zooplankton, the defense against threats from ultraviolet radiation (UV) is a system where phenotypic plasticity and behavioral escape mechanisms function as complementary traits. Freshwater copepods relied mainly on accumulating protective pigments when exposed to UV radiation, but Daphnia showed strong behavioral responses. Pigment levels for both Daphnia and copepods were generally higher at higher latitudes, mirroring different UV threat levels. When released from the UV threat, Daphnia rapidly reduced (within 10 days) their UV protecting pigmentation-by as much as 40%-suggesting a cost in maintaining UV protective pigmentation. The. evolutionary advantage of protective pigments is, likely, the ability to utilize the whole water column during daytime; conversely, since the amount of algal food is generally higher in surface waters, unpigmented individuals are restricted to a less preferred feeding habitat in deeper waters. Our main conclusion is that different zooplankton taxa, and similar taxa at different latitudes, use different mixes of behavior and pigments to respond to UV radiation.
|
|
| 3. |
- Hansson, Lars Anders, et al.
(författare)
-
Instantaneous threat escape and differentiated refuge demand among zooplankton taxa
- 2016
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97:2, s. 279-285
-
Tidskriftsartikel (refereegranskat)abstract
- Most animals, including aquatic crustacean zooplankton, perform strong avoidance movements when exposed to a threat, such as ultraviolet radiation (UVR). We here show that the genera Daphnia and Bosmina instantly adjust their vertical position in the water in accordance with the present UVR threat, i.e., seek refuge in deeper waters, whereas other taxa show less response to the threat. Moreover, Daphnia repeatedly respond to UVR pulses, suggesting that they spend more energy on movement than more stationary taxa, for example, during days with fluctuating cloud cover, illustrating nonlethal effects in avoiding UVR threat. Accordingly, we also show that the taxa with the most contrasting behavioral responses differ considerably in photoprotection, suggesting different morphological and behavioral strategies in handling the UVR threat. In a broader context, our studies on individual and taxa specific responses to UVR provide insights into observed spatial and temporal distribution in natural ecosystems.
|
|
| 4. |
- Sha, Yongcui, et al.
(författare)
-
Diverging responses to threats across generations in zooplankton
- 2020
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 101:11
-
Tidskriftsartikel (refereegranskat)abstract
- Our understanding on how organisms evolutionarily cope with simultaneously occurring, multiple threats over generations is still elusive. In a long-term experimental study, we therefore exposed clones of a freshwater cladoceran, Daphnia magna, to threats from predation and ultraviolet radiation (UVR) during three consecutive parthenogenetic generations. We show that Daphnia can adapt to different sets of threats within three generations through modifying morphology, swimming behavior, or life-history traits. When faced with predator cues, D. magna responded with reduced body size, whereas exposure to UVR induced behavioral tolerance when again exposed to this threat. Such UVR-tolerant behavior was initially associated with a reduced clutch size, but Daphnia restored the reproductive output gradually through generations. The findings advance our understanding on how those common invertebrates, with a global distribution, are able to persist and rapidly become successful in a changing environment.
|
|
| 5. |
- Urrutia Cordero, Pablo, et al.
(författare)
-
Climate warming and heat waves alter harmful cyanobacterial blooms along the benthic-€“pelagic interface
- 2020
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 101:7, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- In addition to a rise in mean air and water temperatures, more frequent and intense extreme climate events (such as heat waves) have been recorded around the globe during the past decades. These environmental changes are projected to intensify further in the future, and we still know little about how they will affect ecological processes driving harmful cyanobacterial bloom formation. Therefore, we conducted a long-term experiment in 400-L shallow freshwater mesocosms, where we evaluated the effects of a constant +4°C increase in mean water temperatures and compared it with a fluctuating warming scenario ranging from 0 to +8°C (i.e., including heat waves) but with the same +4°C long-term elevation in mean water temperatures. We focused on investigating not only warming effects on cyanobacterial pelagic dynamics (phenology and biomass levels), but also on their recruitment from sediments—which are a fundamental part of their life history for which the response to warming remains largely unexplored. Our results demonstrate that (1) a warmer environment not only induces a seasonal advancement and boosts biomass levels of specific cyanobacterial species in the pelagic environment, but also increases their recruitment rates from the sediments, and (2) these species-specific benthic and pelagic processes respond differently depending on whether climate warming is expressed only as an increase in mean water temperatures or, in addition, through an increased warming variability (including heat waves). These results are important because they show, for the first time, that climate warming can affect cyanobacterial dynamics at different life-history stages, all the way from benthic recruitment up to their establishment in the pelagic community. Furthermore, it also highlights that both cyanobacterial benthic recruitment and pelagic biomass dynamics may be different as a result of changes in the variability of warming conditions. We argue that these findings are a critical first step to further our understanding of the relative importance of increased recruitment rates for harmful cyanobacterial bloom formation under different climate change scenarios.
|
|
| 6. |
- Urrutia-Cordero, Pablo, et al.
(författare)
-
Functionally reversible impacts of disturbances on lake food webs linked to spatial and seasonal dependencies
- 2021
-
Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 102:4
-
Tidskriftsartikel (refereegranskat)abstract
- Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (five lakes along a latitudinal gradient in Scandinavia) and time (two seasons, spring and summer) to generate general predictions on how the functioning and composition of multitrophic plankton communities (zoo-, phyto- and bacterioplankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short-term changes in fish presence, and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top-down pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom-up press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top-down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom-up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions.
|
|
| 7. |
- Carlsson, Nils, et al.
(författare)
-
Invading herbivory: The golden apple snail alters ecosystem functioning in Asian wetlands
- 2004
-
Ingår i: Ecology. - 0012-9658. ; 85:6, s. 1575-1580
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the effects of an exotic snail, the golden apple snail (Pomacea canaliculata) on biodiversity and ecosystem functioning in tropical wetland ecosystems. This large snail (up to 80-mm shell height) has invaded large parts of Southeast Asia during recent decades. A survey of natural wetlands in Thailand showed that high densities of the snail were associated with almost complete absence of aquatic plants, high nutrient concentrations, and high phytoplankton biomass, that is, a complete shift in both ecosystem state and function. A field experiment demonstrated that grazing by the snail can cause the loss of aquatic plants, a change toward dominance of planktonic algae, and thereby a shift toward turbid water. Estimates of biologically fixed nutrients released through snails grazing on aquatic plants revealed that phosphorus releases were sufficient to explain the recorded increase in phytoplankton biomass. Hence, our study demonstrates how an herbivore may trigger a shift from clear water and macrophyte dominance to a turbid state dominated by planktonic algae. This shift and the continuing aggressive invasion of this exotic species are detrimental to the integrity and functioning of wetland ecosystems, and to the services these provide in Southeast Asia.
|
|
| 8. |
- Gustafsson, Susanne, et al.
(författare)
-
Increased consumer fitness following transfer of toxin tolerance to offspring via maternal effects
- 2005
-
Ingår i: Ecology. - : Wiley. - 0012-9658. ; 86:10, s. 2561-2567
-
Tidskriftsartikel (refereegranskat)abstract
- Adaptations and, counteradaptations are common in coevolving predatorprey systems, but little is known of the role of maternal transfer of adaptive traits in mediating species interactions. Here, we focused on tolerance against cyanobacterial toxins and asked whether this tolerance was an induced defense developed during Daphnia's lifetime, whether it was a trait that is constantly expressed, and whether such tolerance to the toxin can be transferred to the next generation through maternal effects. These questions were addressed by feeding a single clone of Daphnia magna a diet with and without algal toxin and recording changes in fitness (as intrinsic rate of population increase). Analysis of F1, F2, and F3 generations revealed that the increased tolerance to toxic Microcystis was an inducible defense developed during an individual's lifetime, and that this trait could be transferred from mother to offspring. This maternal effect was expressed in several fitness parameters, including shorter time to maturity and first reproduction, and higher numbers of offspring compared to inexperienced individuals. In some circumstances, such maternal effects may increase population production by up to 40% and may help to stabilize material and energy transfer to higher trophic levels.
|
|
| 9. |
- Hansson, Lars-Anders
(författare)
-
Plasticity in pigmentation induced by conflicting threats from predation and UV radiation
- 2004
-
Ingår i: Ecology. - 0012-9658. ; 85:4, s. 1005-1016
-
Tidskriftsartikel (refereegranskat)abstract
- In a variable and unpredictable environment, phenotypic plasticity in morphology or behavior may considerably improve an organism's protection against environmental threats and thereby its fitness. Here I demonstrate that common freshwater organisms, copepods (Crustacea), show a plastic response by adjusting pigmentation level in relation to two environmental threats: ultraviolet radiation (UV) and predation. The red pigment in copepods, astaxanthin, reduces damage caused by UV radiation, but makes the organism more conspicuous, thereby exposing it to higher predation pressure. In a field survey of six lakes sampled monthly for 16 mo, I quantified UV and predation threat, as well as copepod pigmentation level. The relative threat ratio (UV/predation) was generally lowest during summer and highest during spring; this pattern was paralleled by pigmentation level among copepods. Moreover, the level of pigmentation among copepods in lakes with high predation pressure was lower than among those copepods in lakes with lower risk of predation. In a complementary experimental study performed under constant UV threat, calanoid copepods in the absence of predation threat responded with almost three times higher pigment levels, compared to those with fish present (caged). Hence, the correlative field survey and the mechanistic experiment together suggest that the level of pigmentation in copepods is an inducible and adjustable defense, governed by the aim to improve individual protection against prevailing threats from both predation and UV radiation.
|
|
| 10. |
- Hansson, Lars-Anders
(författare)
-
Synergistic effects of food chain dynamics and induced behavioral responses in aquatic ecosystems
- 2000
-
Ingår i: Ecology. - 0012-9658. ; 81:3, s. 842-851
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to test the hypothesis that temporal differences in food chain composition affect lower trophic levels not only directly, by predation and grazing, but also indirectly, by inducing avoidance behavior. In a field study, the recruitment rate from the sediments to water of two algal species (Gonyostomum semen and Peridinium sp.) was higher at low than at high biomass of herbivorous zooplankton. In complementary laboratory experiments, where abiotic conditions were standardized, the presence of live, as well as dead, herbivores reduced the recruitment rate of both Gondostomum semen and Peridinium sp. These results suggest that some algal species are able to adjust their recruitment behavior in response to the likely risk of being grazed. Together with morphological adaptations (e.g., spines and large size) common among many algal species, such an induced behavioral response is an important adaptation to reduce cell mortality. As shown in this study, this behavioral response may have a profound impact on dominance and succession patterns in algal communities. The high zooplankton biomass observed during the first year of the held study was caused by failed reproduction of the dominant fish species in the lake (roach. Rutilus rutilus). Hence, food chain interactions (low predation on zooplankton, leading to high biomass of herbivorous zooplankton) may act in concert with more indirect, predator-avoidance behavior in structuring the phytoplankton community.
|
|
