| 1. |
|
|
| 2. |
|
|
| 3. |
- Erlinge, Sam, et al.
(författare)
-
Can vertebrate predators regulate their prey?
- 1984
-
Ingår i: The American Naturalist. ; 123:1, s. 125-133
-
Tidskriftsartikel (refereegranskat)abstract
- Whether vertebrate predators can regulate their prey or not has long been a controversial question. At the one extreme it has been claimed that predators have no impact on prey numbers but consume only a doomed surplus (Errington 1946), and at the other that predators strongly interact with their prey causing either stable equilibria or cycles (Tanner 1975; Keith et al. 1977). However,.there are no field studies showing a regulatory effect of predation among vertebrates. Here we report on such a study.
|
|
| 4. |
- Håkansson, P, et al.
(författare)
-
Communal spawning in the common frog Rana temporaria - Egg temperature and predation consequences
- 2004
-
Ingår i: Ethology. - : Wiley. - 1439-0310 .- 0179-1613. ; 110:9, s. 665-680
-
Tidskriftsartikel (refereegranskat)abstract
- Females of the common frog, Rana temporaria, spawn synchronously at communal breeding sites, forming a communal egg mass of individual spawn clumps. A total of four spawning sites were studied. In the centre of the communal egg mass, daily maximum temperature was higher and minimum temperature lower than further out. Spawn clumps in the centre of the communal egg mass developed faster than single spawn clumps. In the centre of the egg masses, some spawn clumps suffered almost total egg mortality. This was probably the consequence of a cold spell with sub-zero temperatures in combination with a tendency for low minimum temperatures in the centre. In a laboratory study, worm leeches, Erpobdella spp., fed readily on eggs of common frog, while horse leeches, Haemopis sanguisuga, hardly ate any eggs. At the spawning sites, most worm leeches were found in single spawn clumps, far from the communal egg mass. Females which spawned late, when most of the spawning was over, preferred to spawn in the centre of the communal egg mass. This suggests that there is a net advantage for eggs in spawn clumps laid in the centre.
|
|
| 5. |
- Lardner, Björn, et al.
(författare)
-
Growth or reproduction? Resource allocation by female frogs Rana temporaria
- 2003
-
Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 137:4, s. 541-546
-
Tidskriftsartikel (refereegranskat)abstract
- The decision how to allocate marginal resources to reproduction and growth can have important effects on associated life-history parameters as well as on population dynamics. In addition to showing variation among individuals in a population, such allocation rules may be either condition-dependent or fixed in different individuals. While many studies on anuran amphibians have focused on egg numbers and egg sizes in females of different sizes, virtually no data exist on the relative allocation of marginal resources to growth versus reproduction. In the laboratory, we therefore offered female common frogs (Rana temporaria) low versus high food rations for a full reproductive cycle, and monitored their growth and later reproductive investment (egg number and egg size the following breeding season). Feeding rates had an effect both on female growth and on egg number and size. There was no trade-off found between the two forms of investment. A flexible allocation rule could not be supported as there was no significant effect of feeding rate on the relative allocation of resources to growth versus reproduction.
|
|
| 6. |
- Loman, Jon
(författare)
-
Breeding phenology in Rana temporaria. Local variation is due to pond temperature and population size
- 2016
-
Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 6:17, s. 6202-6209
-
Tidskriftsartikel (refereegranskat)abstract
- Frog breeding phenology in temperate zones is usually compared to progress of spring temperatures at a regional scale. However, local populations may differ substantially in phenology. To understand this, local climate and other aspects must be studied. In this study, breeding phenology of the common frog, Rana temporaria, in a set of ponds in southern Sweden is analyzed. There was within year a variation of up to 3 weeks in start of breeding among local populations. Water temperature was measured in the ponds, and breeding tended to be earlier in warmer ponds (surprise!). Breeding was also earlier in ponds with a large breeding congregation. Alternative reasons for these patterns are suggested and discussed. There was a large residual variation. The common frog has a wide range of acceptable wintering sites, and I hypothesize that the particular choice by a local population may explain part of this residual variation.
|
|
| 7. |
- Loman, Jon
(författare)
-
Brown frog breeding phenology in south Sweden 1990 – 2017 : Are data subsets robust?
- 2019
-
Ingår i: Herpetological Bulletin. - 1473-0928. ; :147, s. 9-14
-
Tidskriftsartikel (refereegranskat)abstract
- - Field data on breeding phenology of Ranaarvalis and R.temporaria for the period 1990- 2017 in Scania, Sweden are presented and analysed. There was no temporal trend for R.temporaria. ForR.arvalisthe results were mixed, one out of two approaches found a trend to earlier breeding. The lack of a consistent trend in breeding phenology is unsurprising considering that local mean air temperatures in February, March and April showed no significant trends over the study period. To test the robustness of the conclusion, different subsets of the data (years or ponds) were also analysed for trends. For most subsets the conclusions remained the same. Possible bias arising from the choice of which years to include in an analysis of trends is discussed.
|
|
| 8. |
- Loman, Jon, et al.
(författare)
-
Density dependent growth in adult brown frogs Rana arvalis and Rana temporaria - A field experiment
- 2009
-
Ingår i: Acta Oecologica. - : Elsevier BV. - 1146-609X. ; 35:6, s. 824-830
-
Tidskriftsartikel (refereegranskat)abstract
- In species with complex life cycles, density regulation can operate on any of the stages. in frogs there are almost no studies of density effects on the performance of adult frogs in the terrestrial habitat. We therefore studied the effect of summer density on the growth rate of adult frogs during four years. Four 30 by 30 m plots in a moist meadow were used. In early summer, when settled after post-breeding migration, frogs (Rana arvalis and Rana temporaria that have a very similar ecology and potentially compete) were enclosed by erecting a fence around the plots. Frogs were captured, measured, marked and partly relocated to create two high density and two low density plots. In early autumn the frogs were again captured and their individual summer growth determined. Growth effects were evaluated in relation to two density measures: density by design (high/low manipulation), and actual (numerical) density. R. arvalis in plots with low density by design grew faster than those in high density plots. No such effect was found for R. temporaria. For none of the species was growth related to actual summer density, determined by the Lincoln index and including the density manipulation. The result suggests that R. arvalis initially settled according to an ideal free distribution and that density had a regulatory effect (mediated through growth). The fact that there were no density effects on R. temporaria (and a significant difference in its response to that of R. arvalis) suggests it is a superior competitor to R. arvalis during the terrestrial phase. There were no density effects on frog condition index, suggesting that the growth rate modifications may actually be an adaptive trait of R. arvalis. The study demonstrates that density regulation may be dependent on resources in frogs' summer habitat. (C) 2009 Elsevier Masson SAS. All rights reserved.
|
|
| 9. |
- Loman, Jon
(författare)
-
Density regulation in tadpoles of Rana temporaria: A full pond field experiment
- 2004
-
Ingår i: Ecology. - 0012-9658. ; 85:6, s. 1611-1618
-
Tidskriftsartikel (refereegranskat)abstract
- Tadpole density dependence has repeatedly been studied in laboratories and mesocosms, but rarely in natural ponds. The present study manipulated density in three ponds; each pond was divided into one low density section and one high density section. The experiment was run for eight years, switching density treatments within ponds among years. This experimental design cannot definitively separate the experimental density effects from certain lag effects. This problem is discussed. Nonetheless, in all ponds tadpole survival was affected by the density manipulation. The reduced survival of larvae at high density was most pronounced in the pond with the overall highest density. In this pond, the density-dependent mortality almost offset the original, experimental, density difference between sections. Effects on tadpole and metamorph size and development rate were found in those cases in which density-dependent mortality was weak and treatment effects on density persisted to the later stages of tadpole development. However, even if significant, these were generally of small magnitude compared to the variation among ponds and years. 1 suggest that different modes and degrees of regulation among populations of one species of frog are to be expected, not only due to variation in pond quality but also due to variation in the surrounding terrestrial habitat. This may determine the balance between tadpole and adult population regulation.
|
|
| 10. |
- Loman, Jon, et al.
(författare)
-
Does landscape and habitat limit the frogs Rana arvalis and Rana temporaria in agricultural landscapes? A field experiment
- 2009
-
Ingår i: Applied Herpetology. ; 6:3, s. 227-236
-
Tidskriftsartikel (refereegranskat)abstract
- Frogs are often rare or absent from intensively farmed areas. Here we explore the possibility that the landscape and the quality of the terrestrial habitat are unsuitable for these populations. Spawn of Rana arvalis and R. temporaria was introduced into ponds in a south Swedish agricultural landscape in 2003 (eight ponds) and 2004 (ten ponds). Metamorphs emerged from nine (R. a.) and 12 (R. t.) of these. In years following the introduction, spawn was found in five (R. a.) and eight (R. t.) of these 18 ponds. The number of spawn clumps peaked two years after the introduction. Three or four years after the introduction, breeding persisted in only two of the ponds (where both species were breeding). One year later also these populations had also become extinct. In control ponds (ponds within 750 m of the introduction ponds), spawn of R. temporaria was occasionally found but there was no trend, nor any temporal peak in frequency or quantity of spawn in these ponds. There were calling males of both species already one year after the introduction at a few ponds, indicating an unusually early maturation for some individuals. We suggest that the terrestrial habitat in this region is not suitable for the continued presence of populations of R. arvalis and R. temporaria. This may be related to the habitat per se or to the isolation of the populations.
|
|
