Spawning Parvocalanus crassirostris at a high adult density: Explaining low adult population numbers and means for improving their intensive culture

The Janzen–Connell hypothesis is a well-known explanation for why tropical forests have large numbers of tree species. A fundamental prediction of the hypothesis is that the probability of adult recruitment is less in regions of high conspecific adult density, a pattern mediated by density-dependent mortality in juvenile life stages. Although there is strong evidence in many tree species that seeds, seedlings, and saplings suffer conspecific density-dependent mortality, no study has shown that adult tree recruitment is negatively density dependent. Density-dependent adult recruitment is necessary for the Janzen–Connell mechanism to regulate tree populations. Here, we report density-dependent adult recruitment in the population of Handroanthus guayacan, a wind-dispersed Neotropical canopy tree species. We use data from high-resolution remote sensing to track individual trees with proven capacity to flower in a lowland moist forest landscape in Panama and analyze these data in a Bayesian framework similar to capture–recapture analysis. We independently quantify probabilities of adult tree recruitment and detection and show that adult recruitment is negatively density dependent. The annualized probability of adult recruitment was 3.03% ⋅ year−1. Despite the detection of negative density dependence in adult recruitment, it was insufficient to stabilize the adult population of H. guayacan, which increased significantly in size over the decade of observation.

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Evidence of density-dependent oviposition behaviour byListronotus bonariensis(Coleoptera: Curculionidae) in Canterbury pasture

Bulletin of Entomological Research ◽

10.1017/s0007485300026043 ◽

1998 ◽

Vol 88 (5) ◽

pp. 527-536 ◽

Cited By ~ 9

Author(s):

M.R. McNeill ◽

D.B. Baird ◽

S.L. Goldson

Keyword(s):

Biological Control ◽

Field Experiments ◽

Adult Population ◽

Egg Laying ◽

Oviposition Behaviour ◽

Initial Population ◽

Adult Density ◽

Control Effort ◽

Density Dependent ◽

Age Related

AbstractArgentine stem weevil (Listronotus bonariensis) (Kuschel) is a pasture pest ofLoliumspp. in New Zealand and is the target of a classical biological control programme using the parasitoidMicroctonus hyperodaeLoan. However, laboratory experiments have indicated a strong density-dependent egg laying response which may have important implications for the biological control effort. Two field experiments were conducted using a manipulated range of weevil densities within 2.0–2.4 m–2field enclosures and oviposition activity measured by weekly sampling of grass tillers within the enclosures. In both experiments, density had no effect on general oviposition behaviour although the percentage of tillers found to be infested with eggs increased significantly at higher densities. In experiment 1,L. bonariensisexhibited strong density-dependent oviposition with a significant decline in eggs/tiller/female with increasing adult density. An initial population of fiveL. bonariensism−2oviposited 32 times more eggs/tiller/female than 200L. bonariensism−2. By comparison, density-dependent oviposition was absent in experiment 2 with eggs/tiller/female comparable for all densities. The dramatic difference between the two experiments in the expression of density-dependent oviposition was attributed to prevailing spring temperatures during the sampling interval, which in the second experiment were much cooler and delayed the onset of egg laying. It is probable that in experiment 2, oviposition was not regulated by density-dependent cues but limited by temperature and age related mortality in the adult population. The mechanism for density-dependent oviposition, its occurrence in the field and impact on the effectiveness of the parasitoidM. hyperodaeare discussed.

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The demography of recovery of an overexploited bull trout, Salvelinus confluentus, population

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f06-172 ◽

2007 ◽

Vol 64 (1) ◽

pp. 113-126 ◽

Cited By ~ 38

Author(s):

Fiona D Johnston ◽

John R Post ◽

Craig J Mushens ◽

Jim D Stelfox ◽

Andrew J Paul ◽

...

Keyword(s):

Adult Population ◽

Fold Increase ◽

Recovery Process ◽

Data Sets ◽

Adult Density ◽

Life Stages ◽

Bull Trout ◽

Salvelinus Confluentus ◽

Compensatory Response ◽

Density Dependent

An exploited bull trout, Salvelinus confluentus, population experienced a 28-fold increase in adult density during a 10-year period from a minimum of 60 individuals. This demonstrates the extent to which this population was overharvested. Its ability to respond in fewer than two generations to the implementation of zero-harvest regulations suggests this population was growth-overfished not recruitment-overfished. Examination of stock–recruitment relationships of various life stages indicates that recovery of this population was regulated by the density-dependent survival of juveniles in the rearing creek. This compensatory response occurred between egg deposition and age-1 and regulated the number of fish recruiting into the adult population. A second population bottleneck became apparent later in the recovery process when density-dependent survival of the adult population resulted in its approach to an asymptote, highlighting the necessity of long-term data sets for examining these compensatory responses. Results from this study demonstrate the importance of understanding the influence of individual life stages on the ability of overexploited populations such as threatened bull trout to recover and for their future management.

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EFFECT OF AN ANNUAL AND A PERENNIAL CROP ON TROPHIC GROUP DYNAMICS OF NEMATODES

Canadian Journal of Soil Science ◽

10.4141/cjss88-009 ◽

1988 ◽

Vol 68 (1) ◽

pp. 101-109 ◽

Cited By ~ 10

Author(s):

N. G. JUMA ◽

C. C. MISHRA

Keyword(s):

Group Dynamics ◽

Adult Population ◽

Trophic Group ◽

Average Density ◽

Adult Density ◽

Trophic Groups ◽

Perennial Crop ◽

Dominant Group ◽

Plant Parasites ◽

Medicago Sativa L

Adult and juvenile nematode distribution and trophic group dynamics were studied in oat (Avena sativa L.) and alfalfa (Medicago sativa L.) plots of a 5-yr rotation at Breton, Alberta. Nematodes were separated into two groups: (i) adults including the late juveniles and (ii) juveniles. The adults and the late juveniles were further separated into four trophic groups: (i) plant parasites, (ii) microbivores, (iii) miscellaneous feeders and (iv) predators. Adults accounted for 83% of the total population in the oat plot and 79% in the alfalfa plot. There were no significant differences in percent distribution of adults between plots over the season or at a given date. The average density of adults over the season in the oat plot (3.3 × 106 individuals m−2) was greater than that in alfalfa plot (2.1 × 106 individuals m−2, P < 0.001). Adult density in the oat plot increased steadily from 3.2 × 106 to 4.2 × 106 individuals m−2 between July and September. There was a sharp decline after harvest. In contrast, the adult population in the alfalfa plot remained steady over the growing season. Juvenile density showed similar trends as the adults. Distribution of microbivores, plant parasites, miscellaneous feeders, and predators, was 63, 22, 13, and 2% in oat and 51, 34, 13, and 2% in alfalfa plot, respectively. Crop effect on microbivores and plant parasites was significant at P < 0.05. Our study showed that microbivores are the dominant group in cultivated soils and plant parasites build up in the presence of living roots. Key words: Microbivores, miscellaneous feeders, nematodes, plants parasites, predators, trophic groups

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