DYNAMIC THINNING LINES, A UNIVERSAL CONCEPT ON PLAICE NURSERY GROUNDS - - PowerPoint PPT Presentation
DYNAMIC THINNING LINES, A UNIVERSAL CONCEPT ON PLAICE NURSERY GROUNDS . Nash, R.D.M. 1 , Geffen, A.J. 1,2 , Witte, J. IJ. 3 , and van der Veer, H.W. 3 1 Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway 2 Department of Biology,
Nash, R.D.M.1, Geffen, A.J.1,2, Witte, J. IJ.3, and van der Veer, H.W.3
1Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway 2Department of Biology, University of Bergen, PO Box 7800, 5020 Bergen, Norway 3Royal Netherlands Institute for Sea Research, NIOZ, PO Box 59, 1790 AB Den Burg Texel, The Netherlands
The dynamics: Numbers of individuals on a nursery ground seasonally increase, individual weights increase, total biomass increases, at some point density begins to fall and then total biomass decreases until the influx of the new year class and the cycle starts again. Numbers Individual weight Total biomass Time (April to December) Specifically considering the cases where the population reaches the carrying capacity
From plant ecology: Crowded, even-aged monocultures approach and then track along a line.
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Where: w = mean weight, d = population density and c = constant Total weight of the population continues to increase as individuals grow, self-thinning
cessation in increase. Total weight then remains constant i.e. ‘carrying capacity’ is reached and the slope becomes –1 on a log-log plot.
In diagrammatic form (plants): Log density Log mean weight Initial growth Self-thinning boundary Slope = -3/2 Resource limitation, structural or physiological constraint Slope = -1 (Constant biomass)
The self-thinning rule: as applied to animal populations
Expected that a constant biomass/carrying capacity might be applicable i.e. slope = -1. However, relating the slope to metabolic rates i.e. raised to 0.75 or a slope of –1.33 is probably more applicable for mobile animals. This gives:
Proviso: Assumes that the food/resource (F) input to the population remains constant throughout the growth of the cohort. However, the possibility that F remains constant for animal populations is much less likely.
Adapted from Begon et al. 1986 Log density Log Mean weight dF +ve dt Self-thinning in animal populations: Theoretical considerations Amount of food increases with time. Steepens the s-t line (<-4/3 e.g. –3/2, -2 etc)
dF –ve dt Consumption outstrips food growth Log Mean weight Log density Less steep (>-4/3 e.g. –1) Self-thinning in animal populations:Theoretical considerations Adapted from Begon et al. 1986
Also: dF/dt can change due to the behaviour of the population e.g. territoriality or migration
Boundary lines Species boundary lines: ‘a line beyond which combinations of density and mean weight are not possible’ (see Weller 1990, Begon et al. 2006) Essentially the carrying capacity of the environment.
Food-limited cohorts The carrying capacity is determined by the balance between growth and mortality
Self-thinning in food-regulated populations [energetic equivalence theory]
F
m βg
Growth (g) Mortality (m) Log (w) Log (N)
Carrying capacity is where βg=m (intercept). Lower food production affects either βg or m. Equilibrium energy flow (F) is lower in habitats with lower food production. If food production keeps changing then the slope will
environments the slope is not constant Progress along the thinning lines are equal.
Bohlin et al. 1994
The case of energy flow (F) varying with body size
Log (w) Log (F/k) Log (N) Curvilinear thinning lines Diet changing with body size Food for intermediate body sizes having a higher rate of production
Bohlin et al. 1994
Why choose juvenile flatfish and plaice in particular?
Port Erin Marine Laboratory
Kristineberg Marine Research Station
NIOZ Dunstaffnage Marine Laboratory
28-Jan 25-Feb 25-Mar 22-Apr 20-May 17-Jun 15-Jul 12-Aug 9-Sep 7-Oct 4-Nov 2-Dec 30-Dec
Day of year
12 16 20 24 28
Loge Abundance
Hatch Metamorphosis Begining July Start Age 1
Potential Egg Production
PELAGIC DEMERSAL
Eggs Larvae Settlement period Nursery ground Over-wintering
SSB
Early life history trajectory for North Sea plaice (Pleuronectes platessa)
From : Beverton & Iles (1992) Beverton (1995) North Sea
Irish Sea
Nash & Geffen (20??)
Dynamics of a nursery ground Supply of larvae/juveniles Time Increasing size
Decrease in abundance due to mortality Decrease in abundance due to emigration Phases (idealised):
Inter-annual variations on nursery grounds
Log density Log mean weight
Low production year High production year Differences between nursery grounds
Log density Log mean weight
Low carrying capacity High carrying capacity
Expected trajectory of log mean weight and log population density
Settlement Log density Log mean weight Self-thinning Emigration Food limitation? Growth
Plaice nursery grounds with time series of abundance and mean weights
0.001 0.01 0.1 1 10 100
Density (m-2)
0.01 0.1 1 10 100 1000
Mean weight (g)
Tralee (open) PE Bay (closed) 1986 1987 1988 1989 1995 1996 1997 PE 1995 PE 1996 PE 1997 PE 1998 PE 1999
Expected slope = -1.33
Po Port Erin Bay
0.001 0.01 0.1 1 10 100
Density (m-2)
0.01 0.1 1 10 100 1000
Mean weight (g)
Slope = -1.31
Tr Tralee Bay (S (Scotland)
0.001 0.01 0.1 1 10 100
Density (m-2)
0.01 0.1 1 10 100 1000
Mean weight (g)
Slope = -1.26
Nash et al. 2007 MEPS 344
0.001 0.01 0.1 1 10 100
Density (per sq m)
0.001 0.01 0.1 1 10 100 1000
Average weight (AFDW) per plaice (g)
Swedish Bays 1978 1979 1991 1992 Self-thinning 1991 Self-thinning 1992
Slope = -1.46 Slope = -1.09 Other plaice nursery grounds Filey Bay – density varies x30 Firemore Bay – density varies x6
y = -0,778x - 0,3228 R² = 0,7611
0,5 1 1,5 2
0,5 1 1,5
Data Thinning Constant biomass Linear (Data)
Drop trap Swedish Beaches (1978, 79, 91, 92)
Dutch Wadden Sea (1975-86, 1991, 1993-2002, 2007, 2009, 2014)
0,01 0,1 1 10 100
0,0001 0,0010 0,0100 0,1000 1,0000 10,0000 Mean weight (g) Density (m-2)
y = -1,371x - 1,6416 R² = 0,5469
0,5 1 1,5 2
0,5 1
All data
y = -1,5681x - 1,4881 R² = 0,4154
0,5 1 1,5 2
0,5 1
1970s
y = -1,7151x - 1,9001 R² = 0,4697
0,5 1 1,5 2
0,5 1
1980s
y = -1,3426x - 1,8036 R² = 0,7464
0,5 1 1,5 2
0,5 1
1990s
y = -1,1195x - 1,565 R² = 0,6942
0,5 1 1,5
0,5 1 1,5
2000s
At a given density there was a reduction in mean weight of: 55% – between 1970s and 1980s 68% – between 1980s and 1990s But an increase 26% - between 1990s and 2000s Overall a reduction of: 80% - between 1970s and 2000s
Varying boundary lines?
0,0 1,0 2,0 3,0 4,0
0,0 0,5 1,0 1,5
Log Mean weight (g) Log Density (m-2)
Tralee Swedish DT 1970s PEB 1980s 2000s 1990s
Comparisons between nurseries – a question
Location Thinning intercept Max density (m-2) Tralee 1,02 14,4 Swedish 0,25 10 PEBay
3 Filey Bay 1,2 Firemore Bay 1,2 WS2000s
0,8 WS1990s
0,8 WS 1970s
1 WS 1980s
0,4
Maximum densities observed on the nursery grounds
Self-thinning (a single species consideration) A cohort over time, ages and the individuals grow. The resource requirements i.e. space and food increase and thus competition will also increase. The risk of dying increases. If individuals die, density decreases, competition decreases which affects growth – this in turn affects competition and thus growth and so the cycle continues. In animal populations – the ‘rules’ seen in plant populations may be more questionable due to: Variable resource supply Possible other factors e.g. territoriality etc rather and only the food supply Begon et al. 2006 However, they provide a framework for modelling density, with a growth (and thus mortality rates) on nursery grounds, through the summer and autumn months.
The dynamics of nursery grounds can be very complex with numerous inter-specific interactions occurring
Predatory gadoids
Competitors Residents
Predatory crustaceans
considerable variability in density