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| 2. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Do intruding predators and trap position affect the reliability of catches in activity traps?
- 1992
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 239:3, s. 187-193
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Tidskriftsartikel (refereegranskat)abstract
- Forty lakes in Sweden and Finland were sampled in 1990 with activity traps to evaluate the effects of trapped predators on invertebrate catch. Vertebrate (fish, newts) and invertebrate (leeches, dragonflies, water beetles, backswimmers and water scorpions) predators were considered separately. Invertebrate predators affected neither the abundance nor the taxonomic diversity of the catches. Vertebrate predators had no effect on the abundance but reduced the taxonomic diversity of the catches significantly. Thus, vertebrate predators are a possible source of bias in activity trap catches, but oily concerning taxonomic diversity. Within the depth gradient studied (0.25-0.75 m), trap position (suspended in mid-water versus on the bottom) did not affect the percentages of nektonic and benthic invertebrates in the catches. The relative abundance of all taxa was similar in the catches from different trap positions, but the relative abundance of the most numerous taxa as well as the diversity of the catches differed between trap positions. We conclude that both mid-water and bottom traps are suitable for monitoring aquatic invertebrates, and that bottom traps may be preferred for practical reasons.
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| 3. |
- Elmberg, Johan, 1960-
(författare)
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Factors affecting male yearly mating success in the common frog, Rana temporaria
- 1991
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Ingår i: Behavioral Ecology and Sociobiology. - 0340-5443 .- 1432-0762. - 0340-5443 ; 28:2, s. 125-131
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Tidskriftsartikel (refereegranskat)abstract
- The mating behavior of the European common frog, Rana temporaria, was studied experimentally. Female body length was correlated with body mass as well as with fecundity. However, males showed no mating preference with regard to either female body length, body mass, or fecundity. In successive multiple matings, male readiness to re-mate as well as fertilization success did not vary among the first four matings. Further, fertilization success was not correlated with either the number of days since the previous fertilization, water volume in the experimental container, testes mass, female/male body length ratio, or female fecundity. However, there was a positive correlation between fertilization success and male fat reserve status. Sexual competition and mating patterns were studied in tanks in which operational sex ratio (OSR) and male density were manipulated, and time for sexual competition was allowed to vary. Successful take-overs and nonrandom mating (large male advantage) were observed only at a combination of a four-fold male bias in OSR and an unnaturally high male density (30-50/m2). I argue that in natural populations of Rana temporaria: (1) There is considerable intraspecific variation in the opportunity for sexual competition, (2) OSR influences mating pattern more than male density and time (duration of the prespawning period), and (3) nonrandom mating should be rare.
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| 4. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Factors affecting species number and density of dabbling duck guilds in North Europe
- 1993
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Ingår i: Ecography. - 0906-7590 .- 1600-0587. - 0906-7590 ; 16:3, s. 251-260
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Tidskriftsartikel (refereegranskat)abstract
- We addressed how species number and pair density in guilds of co-existing species is related to habitat structure, and to the abundance and diversity of food resources. using the assemblage of seven species of dabbling ducks (genus Anas) breeding in 60 lakes distributed over six regions in temperate north Europe. Partial correlation and multiple regression revealed that species richness was best predicted by habitat structural diversity as indexed by a principal component analysis based on 18 vegetation and lake characteristics, and by the abundance of aquatic and emergent prey. We found no effect of lake size or prey size diversity on species richness. Pair density was correlated with the percentage of shoreline with horsetails (Equisetum), by habitat structural diversity and by the abundance of emergent invertebrate prey. Neither prey size diversity nor abundance of aquatic prey correlated with pair density. Species richness and pair density in North European duck guilds vary both with habitat structure and prey availability.
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| 5. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Intraspecific variation in calling, time allocation and energy reserves in breeding male common frogs Rana temporaria
- 1991
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Ingår i: Annales Zoologici Fennici. - 0003-455X .- 1797-2450. - 0003-455X ; 28:1, s. 23-29
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Tidskriftsartikel (refereegranskat)abstract
- Time allocation during breeding was studied in unmated male common frogs Rana temporaria Linnaeus in three populations along a gradient of altitude, climate and length of feeding season. The length of the breeding period decreased with increased altitude. All three populations had low activity levels (0-33% of the time during peak chorusing). Peak chorusing in the lowland population was due to more males participating in the chorus, and not to increased individual calling activity. An increase in mating effort at this time was nevertheless indicated by the males 'using more time for moving in the pond. At both montane localities, males called more sparsely, and not at all at night. During peak chorusing, calling and moving males became significantly rarer with increased altitude. Aggressive males were significantly rarer in the alpine population. Between-locality variation was evident in fat reserves after hibernation and during breeding; the relative fat body mass was significantly higher in lowland males than in mid-altitude and alpine males. We discuss male mating activity (here: calling, mate searching and aggression) in ultimate terms as a trade-off between mate acquisition and survival.
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| 6. |
- Elmberg, Johan, 1960-
(författare)
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Long-term survival, length of breeding season, and operational sex ratio in a boreal population of common frogs, Rana temporaria L.
- 1990
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Ingår i: Canadian Journal of Zoology. - 0008-4301 .- 1480-3283. - 0008-4301 ; 68:1, s. 121-127
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Tidskriftsartikel (refereegranskat)abstract
- A population of individually marked adult Rana temporaria was studied during the breeding season in 1979–1988 in east-central Sweden. Annual return rate averaged 31% (range 16–51%) in males and 16% (range 5–33%) in females. Return rate was not size dependent but increased with every successful previous hibernation, indicating an increased survival rate with age. Return rate was not correlated with winter harshness. Once adult, males had on average 1.5 (maximum 6) seasons with the possibility of reproducing. Corresponding values for females were 1.4 and 4. Mean length of the breeding season was 20 (SD = 2) days. Calling generally started at water temperatures below 3 °C. The lowest spawning temperature was 1 °C. Average temperatures at spawning onset and peak spawning were 5 and 6 °C, respectively. Large males tended to arrive earlier at the pond than small males. Males arrived earlier and stayed longer than did females. The overall population sex ratio was close to unity. The operational sex ratio (OSR) varied during the breeding season, averaging 0.54 (one female to two males). No male was observed to mate more than once per season. I argue that survival selection is more important to male lifetime mating success than is competition in the breeding pond (sexual selection as affected by OSR and length of the breeding season).
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| 7. |
- Elmberg, Johan, 1960-
(författare)
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Ovarian cyclicity and fecundity in boreal common frogs Rana temporaria L. along a climatic gradient
- 1991
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Ingår i: Functional Ecology. - 0269-8463 .- 1365-2435. - 0269-8463 ; 5:3, s. 340-350
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Tidskriftsartikel (refereegranskat)abstract
- Hypotheses that the patterns of energy storage, ovarian development and fecundity change along a climatic gradient were tested. Data from adult female common frogs Rana temporaria L. were collected in three study areas from mixed boreal lowland forest to alpine heath. There were no consistent altitudinal trends in body length or weight. Age, however, increased with altitude. During the feeding season, the rate of primary deposition of energy in the fat bodies was higher in mid-altitude than in lowland females. Relative ovary weight increased faster in alpine heath and mid-altitude frogs than in lowland frogs. There were no indications of an ovarian resting period. Rather, with increased altitude the oocytes for next year's reproduction tended to have entered the vitellogenic growth phase even before oviposition; possibly this was an adaptation to a short feeding season. Body length and fecundity were exponentially related in the lowland and the mid-altitude study areas. The relationship between body weight and fecundity appeared to be linear in at least the lowland population. Fecundity per gram body mass increased with age. Although differences between study areas were found, there was no consistent altitudinal trend in either absolute or size-relative fecundity. Fecundity varied between years as well as between populations. A negative correlation between relative liver weight and fecundity indicated a high cost to reproduction. Nevertheless, skipping years of reproduction, a phenomenon suggested to occur primarily in resource-poor environments, was rare.
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| 8. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Patterns of lake acidity and waterfowl communities
- 1994
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Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. - 0018-8158 ; 279-280:1, s. 201-206
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Tidskriftsartikel (refereegranskat)abstract
- Breeding waterfowl communities were studied in 28 lakes in three areas in North Europe, along gradients of acid precipitation and alkalinity that result in lake conditions ranging from unaffected to strongly acidified. Acidic lakes had generally sparser and less complex vegetation, and fewer invertebrates were caught in activity traps. There was neither correlation between pH and waterfowl species richness (genus Anas, family Anatidae, and waterfowl sensu latu tested separately), nor between pH and waterfowl diversity (Simpson's index). Further, pH and waterfowl population density (genus Anas, family Anatidae, and waterfowl sensu latu) were not correlated, but when functional rather than taxonomic groups were considered, pH and relative abundance of fish-eating species (Gaviidae and Podicipedidae) were correlated. However, the relative abundance of Bucephala clangula, a diving duck that may compete with fish for food, was not correlated with pH. Although individual species may be affected, community level responses of waterfowl to acidity are either absent or hard to detect at our sites.
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| 9. |
- Elmberg, Johan, 1960-, et al.
(författare)
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Relationships between species number, lake size and resource diversity in assemblages of breeding waterfowl
- 1994
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Ingår i: Journal of Biogeography. - 0305-0270 .- 1365-2699. - 0305-0270 ; 21:1, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- Breeding waterfowl, habitat diversity and food diversity were studied in 31 boreal lakes in Finland and Sweden. Lakes were 2-48 hectares in size, and had zero to eleven waterfowl species each. In all, sixteen species of Gaviiformes, Podicipediformes, Anseriformes and Fulica were recorded. The observed species distribution deviated from the 'null' expectation derived from a model of random placement, indicating a low importance of lake area per se. However, lake area was found to be a better predictor of species number than was length of shoreline, and lake area-species number regressions gave values between 0.255 and 0.345. We further evaluated 'the area per se (sampling)' hypothesis and 'habitat diversity' hypothesis separately by multiple stepwise regressions, in which lake area explained most of the variation in species number in species dependent on the lake for brood-rearing. Richness of more mobile species and of all species was best explained by the number of prey taxa encountered in the lake.
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