The Effects of Intraspecific Competition among Varying
Groups of Marigolds
Tiffany Landis, Undergraduate Student, Department of Biology, Tennessee
Technological University, Cookeville, TN 38505
February 8, 2006
2
Table of Contents
Project Summary
Introduction
Methods and Material
Expected Results and Benefits
Project Timeline
Literature Cited
Budget
Project Summary
Problem: Does intraspecific competition affect the alyssums vitality?
3
Objective/ Hypothesis: To determine if Intraspecific competition affects plant growth.
Intraspecific competition foes affect density and growth of Marigold plants.
How I plan to accomplish my goal: Planting varying densities of Marigolds to
determine if intraspecfic competition affects their growth.
Expected benefits and Results: This should be beneficial to farmers and gardeners who
will then know that you cannot plant a bunch of plants together or they will compete each
other and eventually one will out compete the other and cause plants to be either stunted
in growth or just die.
Introduction
Competition for resources is what drives natural selection. As Darwin stated
4
“Only the fit survive.” Those species that are best suited for survival are the ones that
can out compete with other species for the same-shared resources. There are two forms
of competition interspecific competition and intraspecific competition. Interspecific
competition occurs when two or more species compete for some limited resource. When
one species is a better competitor in this case they negatively effect the other species,
this can cause the population of the other species to decline in population size.
Intraspecific competition occurs between members of the same species. They will both
compete for the same limited resource. A consequence of intraspecific competition would
be that when the population becomes more dense the survival and/or reproduction rates
of the individuals declines. “Competition, either among members of the same or different
species may have broad effects on plant community structure. The more crowded a
population the more competition there is for resources.” (Tansley, 1917)
In many cases intraspecific competition will occur because of the need to compete for the
same shared resource, such as the need for space. “Spatial arrangement of plants in a
community can be an important determinant of species coexistence and biodiversity”
(Stoll et al, 2001). In this study plants were grown in two densities either randomly or
intraspecifically aggregated. Stoll and his colleague Prati concluded that the
Competitively superior species had a lower biomass in the aggregated distribution than in
the random distribution at high densities. “The data supported the hypothesis that the
spatial distribution of plants profoundly affects competition in such a way that weaker
competitors increase their fitness while stronger competitors are suppressed when grown
in the neighborhood of co specifics” (Stoll et al, 2001).
One of the central questions in ecology is how important is competition among
5
individuals within species (intraspecific) in determining the fitness of individuals in
populations. One way to address this question is to grow organisms in single species
groups in the laboratory. Plants that lack the proper nutrients will not have what it takes
to survive. Day and her colleagues found that when plants are nutrient poor soil they
would be smaller compared to plants in nutrient rich soils. They also found that mortality
was higher in nutrient rich soils then in nutrient poor soil. Thus, one can conclude from
their findings those plants will be of greater in abundance in nutrient rich soils and more
susceptible to competition, which those plants in the nutrient poor soil will not have to
compete because the nutrients are already limited.
In my experiment with Alyssum I looked to intraspecific competition to
determine if plants with more competitors will end up smaller than plants grown with
fewer competitors. The idea being that competitors will take up light and nutrients and
leave a lot less of those nutrients for other plants. My null hypothesis being that no matter
the density, plant weight and height will reflect no difference among the varying
densities. As one species competes, the other must also in order to survive. I knew that
the most fit will survive and through the experiment I conducted I will try to provided
evidence to support my hypotheses.
Methods and Materials
I obtained six pots and labeled them according to the number of seeds in each
6
pot. The pots were also labeled with our group name to make sure there was not any
confusion as to whose plants to belong to whom. The plants were kept in a sunroom and
watered regularly. Each of the six pots was filled with soil until it came to about one
centimeter from the top of the pot. I obtained Marigold seeds and planted the following
densities of seeds in each pot: 3, 5, 10, 18, 34, or 68 seeds. After germination, the plant
populations were thinned to 2, 4, 8, 16, 32, or 64 plants per pot. When then placed more
soil on top of the seeds and watered them. Each week we measured the number of leaves
on each plant in each pot, heights of the plant stems, and number of flowers on each plant.
We then gathered detailed information from each pot number of plants, weights of
plant stems, number of leaves and length of stems. We obtained stem weights of the
plants by clipping out the plants at soil level, clipping off the leaves and placing them on
a scale.
Expected Results and Benefits
I expect that intraspecific competition will affect the growth of plants and that they will
7
Compete with each other for the same shared resource. This should be beneficial to
farmers and gardeners who will then know that you cannot plant a bunch of plants
together or they will compete each other and eventually one will out compete the other
and cause plants to be either stunted in growth or just die.
8
Project Timeline
Planted seeds
and watered
them
Watered plants
and took
measurements
Watered Plants
and took
measurements
Week 1
Week 3
Week 5
Week 2
Week 4
Week 6
Watered plants and
took measurements
Watered plants
and took
measurements
End of Projectcollected
measurements
9
Literature Cited
Aguiar, M.R., Lauenroth, W.K. and Peters, D.P. 2001. Intensity of intra- and
interspecific competition in coexisting shortgrass species. Journal of Ecology
89: p.40.
Day K. J., Hutchings M.J. and John, E.A. 2003. The effects of spatial pattern of nutrient
supply on yield, structure and mortality in plant populations. Journal of Ecology
91: pp.541-553
Siemens, D.H., Garner, S.H.; Mitchell-Olds, T. and Callaway, R.M. 2002. Cost of
defense in the context of plant competition: Brassica rapa may grow and
defend. Ecology 83: pp 505-518.
Stoll, P. and Prati, D. 2001. Intraspecific Aggregation Alters Competitive Interactions In
Experimental Plant Communities Ecology 82: p319.
Tansley, AG. 1917. On competition between Gallium saxatile L. and Gallium sylvestre
pll. on different types of soil. J. Ecology. 5:173-179.
10
Budget
Budget
Potting Soil
Marigold Seeds
Balance
6 Flower Pots
$2.50
$2.00
$31.00
$24.00
11
12
13
14