Community Ecology BCB331 Mark J Gibbons, Room 4.102, BCB Department, UWC Tel: Image acknowledgements –

NICHE Definition In one dimension Survival Growth Reproduction Environmental Gradient e.g. Temperature Performance or Abundance Temperature range over which a variety of plants can achieve net PHS at low light intensity y (Pisek et al., 1973, In: temperature and Light, Prect et al. (Eds), pp Springer)

FUNDAMENTAL NICHE Species B Environmental Condition or Resource Definition Species A Environmental Condition or Resource REALISED NICHEDefinition Species B Species A Environmental Condition or Resource Inter-specific Interactions – competition, predation, mutualisms

Competition normally (BUT NOT ALWAYS) occurs between congeneric species WHY? Tribolium confusum T. castaneum Flour Beetles

Types of Competition Exploitation - Individuals interact with each other indirectly through resource exploitation Bombus appositus Bombus flavifrons Interference - Individuals interact with each other directly

Observations on the outcomes of competitive interactions Exclusion from particular habitats Coexistence

Practical – Niche overlap in four co-existing Rhus species Rhus crenata Rhus glauca Rhus laevigata Rhus lucida

Symmetry and Asymmetric Competition Balanus died of exposure Overgrowth of Chthamalus by Balanus Balanus > Chthamalus angustifolia > latifolia Typha angustifolia Typha latifolia Depth Together Grace and Wetzel (1998) Aquatic Botany 61: Alone

Under what circumstances do interactions lead to co-existence or competitive exclusion?

Competitive Exclusion or Coexistence Lotka-Volterra Models of inter-specific competition Cast your mind back to BDC222 S-Shaped Growth Curves N - Shaped K N t+1 = N t. R / {1 + [N t.(R-1)/K]} Appropriate for populations displaying discrete breeding For populations displaying continuous breeding d N d t = r.N. (1 – N) K N t+1 - N t t 1 – t 0 = 1 K - N K Intrinsic rate of natural increase N t+1 = N t + r.N t K - N K

N t+1 = N t + r.N t K - N K K Incorporates intra-specific competition Replace with something that also incorporates inter-specific competition Suppose that 4 individuals of species 2 have the same competitive effect on species 1, as one individual of species 1 The total competitive effect on species 1 (inter- and intraspecific) will be (N 1 + N 2.1/4) individuals of species 1. The constant (1/4 – in this case) is referred to as the competition coefficient and is given the symbol α, and it measures the per capita competitive effect of one species on another. In this case, α 1,2 = per capita effect of species 2 on species 1 = 0.25 Multiplying N 2 by α 12, converts N 2 into the number of N 1 equivalents.

α 12, > 1 means that an individual of species 2 has more of a competitive effect on an individual of species 1, than does species 1 itself: i.e. interspecific competition is stronger than intraspecific competition α 12, < 1 means that an individual of species 2 has less of a competitive effect on an individual of species 1, than does species 1 itself: i.e. intraspecific competition is stronger than interspecific competition SO…. N 1 = Population size of species 1 N 2 = Population size of species 2 K 1 = Carrying capacity of species 1 r 1 = population growth rate of species 1 α 1,2 = per capita effect of species 2 on species 1 N 1,t+1 = N 1,t + r 1.N 1,t K 1 – N 1,t – α 12 N 2,t K1K1 N t+1 = N t + r.N t K - N K Species 1

N 1 = Population size of species 1 N 2 = Population size of species 2 K 2 = Carrying capacity of species 2 r 2 = population growth rate of species 2 Α 2,1 = per capita effect of species 1 on species 2 N 2,t+1 = N 2,t + r 2.N 2,t K 2 – N 2,t – α 21 N 1,t K2K2 Species 2 Likewise N 2,t+1 = N 2,t + r 2.N 2,t K 2 – N 2,t – α 21 N 1,t K2K2 N 1,t+1 = N 1,t + r 1.N 1,t K 1 – N 1,t – α 12 N 2,t K1K1 These then are the basic Lotka-Voltera equations

Open a spreadsheet in MSExcel How do different values of r, K, N 0 and α xy influence the outcomes of species interactions? Set a parameter matrix up as follows: labels in ROW 1, values in ROW 2 At this stage, make both species equal to each other in all respects Next – project the two populations into the future for 50 time units (using the previous equations), making reference to the values in the above parameter matrix Leave blank for the moment

Plot the two populations on a line graph It should look something like this: both populations co-exist This is an unrealistic example. WHY? In the “Outcome” column of the parameter matrix, enter CoE – species coexistence To look at how different values of r, K, N 0 and α xy influence the outcomes of species interactions, you must change the values in the parameter matrix, and note the response of the two populations on the graph.

Copy the values of the parameter matrix down, and adjust the values of the different cells in different trials. Note the outcomes in each case… So…….. Suggestions To start off with, only change 1 value and keep the others the same What happens if you adjust more than one value? Under what conditions do the two populations co-exist? What role does r play in determining the competitive outcome? Under what conditions do N 0 or K play an important role in influencing the outcome of competition?

N1N1 N2N2 Species 1 Yes – but perhaps better summarised in a different way If you construct a figure showing all possible outcomes of N 2 on N 1 for species 1, for a given r, k and α xy you will end up with a figure that looks like this You should have worked out that varying r made no difference to the eventual outcomes of the competitive interactions BUT – varying the other parameters did Was there a pattern to the results? The pink line represents the line along which there is neither an increase nor a decrease in the abundance of species 1: Zero Net Growth Isoline (ZNGI) Species 1 increases in numbers if it occurs to the left of the ZNGI, but decreases in numbers if it is to the right of the ZNGI

N1N1 N2N2 Species 2 Similarly for species 2 In order to draw a ZNGI for species 1, N 1,t+1 = N 1,t N 1,t+1 = N 1,t + r 1.N 1,t K 1 – N 1,t – α 12 N 2,t K1K1 Therefore 0 = r 1.N 1,t K 1 – N 1,t – α 12 N 2,t K1K1 becomes N 1,t = N 1,t + r 1.N 1,t K 1 – N 1,t – α 12 N 2,t K1K1

N1N1 N2N2 Species 1 K1K1 K 1 α 12 0 = r 1.N 1,t K 1 – N 1,t – α 12 N 2,t K1K1 This is true IF r 1 = 0, or IF N 1,t = 0 BUT…. Also true if 0 =K 1 – N 1,t – α 12 N 2,t Rearranging: K 1 – α 12 N 2,t N 1,t = This equation is similar to that for a straight line: Y = C + m X IF N 1,t = 0 α 12 Then N 2,t = K 1 Then N 1,t = K 1 IF N 2,t = 0 and

K1K1 K 1 α 12 K2K2 K 2 α 21 K1K1 K 1 α 12 K2K2 K 2 α 21 Need to fuse the ZNGI for both species and examine the outcomes of the joint population Joint population Lines are vectors – direction of number flow Individual populations of different species

There are four different ways that the ZNGI can be arranged – and the outcome of the competitive interaction will be different in each case

Here K1K1 K 2 α 21 > AND K 1 α 12 K2K2 > Intra-specific effects of species 1, greater than inter-specific effects of species 2 Intra-specific effects of species 2, less than inter- specific effects of species 1 What is the OUTCOME? Species 1 out-competes Species 2 TRY IT OUT Make sure that α 21 is >1 K1K1 K 2 α 12 >K2K2 K 1 α 21 < INTER- INTRA-

Here K2K2 K 1 α 12 > AND K 2 α 21 K1K1 > Intra-specific effects of species 2, greater than inter-specific effects of species 1 Intra-specific effects of species 1, less than inter- specific effects of species 2 What is the OUTCOME? Species 2 out-competes Species 1 TRY IT OUT Make sure that α 12 is >1 K1K1 K 2 α 12 <K2K2 K 1 α 21 >

Here K1K1 K 2 α 21 > AND Inter-specific effects of species 1, greater than intra-specific effects of species 2 Inter-specific effects of species 2, greater than intra-specific effects of species 1 What is the OUTCOME? Unstable equilibrium – varies with N 0 K2K2 K 1 α 12 > A situation whereby inter-specific competition is stronger in both species than intra- specific competition is seen in allepopathy TRY IT OUT Make sure that α 12 AND α 21 are >1 K1K1 K 2 α 12 <K2K2 K 1 α 21 <

Here AND Intra-specific effects of species 1, greater than inter-specific effects of species 2 Intra-specific effects of species 2, greater than inter-specific effects of species 1 What is the OUTCOME? Stable coexistence at equilibrium K 2 α 21 K1K1 > K 1 α 12 K2K2 > TRY IT OUT Make sure either that α 12 AND α 21 are <1 K1K1 K 2 α 12 >K2K2 K 1 α 21 >

THE END Image acknowledgements –