Diversity and Pollination Success Rate of
Flowers in the Science Hall Prairie
Introduction
Pollination is a very important biological process and is an ecosystem service provided
by animals. The result of pollination on plants is a major contributor to the food produced
around the world. The production of 39 of 57 leading crops increases in the presence of
pollinating animals and insects which is 35% of global food consumption. (Klein et al. 2007) On
a fundamental level, pollination is the transportation of pollen within flowers, or from flower to
flower by pollinators such as birds, bees, beetles, and moths, or by the wind. (URL 1) Pollinators
are the animals and insects that work to fertilize plants so they are able to reproduce and develop
a large seed set (the amount of seeds produced by a plant). The mechanisms of the pollinators
depend on their complex behavior patterns and are not easily emulated by means of artificial
devices, but if it were to be imitated through mechanical means it would cost over one million
dollars per year to be done. (Solomon 1971) Therefore, the seasonal work of pollinators is a large
benefit to the global economy.
In order for pollination to thrive, there are numerous factors and variables that can play a
role in pollination success. The principle factor that can affect pollination is the presence of
pollinators. Some pollinators, such as bumble bees are on the decline in regards to their
population size. This decline is due to the effects of pesticides and the destruction of their habitat
by humans. (Huang 2012) When there is not a demand on the pollinator population, specifically
honey bees, there are other factors that play a role in pollination; one important aspect is weather.
Honey bees are most likely to pollinate when temperatures are above 65 F and winds are no
more than 10 miles per hour. (URL 2)
The last factor of pollination that will be discussed is in regards to the size of the prairie
or area in need of pollination. In order for pollination to persist at a large level, natural habitats
and landscapes must be present in all types of urban areas. The presence of natural landscapes
attracts more pollinators to the area, and they are likely to pollinate and help maintain a steady
diversity of the plant community and seed set of the plants present.
A common natural landscape that does not require much maintenance is a tall grass
prairie. As stated before, pollinators are animals but the most common biotic pollinators of tall
grass prairies are insects. Pollinators are more likely to visit tall grass prairies that are larger in
patch size than smaller patch sizes. This is because having more resources in a closer area will
minimize flight costs to travel further to other flower patches. (Zorn-Arnold 2007).
The objectives of this study are to examine: (i) diversity of plants and how they change
with the seasons, and (ii) the effectiveness of pollinators in two common prairie plants, Purple
Coneflower and Black-Eyed Susan in the Loras Campus Hall Prairie remnants, Dubuque, Iowa.
Success of pollinators was examined by pollinator foraging observations, seed production, and
seed viability. The comparison between insect pollinated and hand-pollinated flowers is a main
component of the analysis for pollinator success the plants. A random subset of seeds were cold
stratified and germinated from the two plant species in order to determine the viability of the
seeds.
Methodology
Plant Diversity
The first phase of the research was to examine plant diversity and classification of the
plants that are present in the Science Hall Prairie. The diversity of the plant species was obtained
by dividing the prairie into transects every two meters; these transects ran parallel to each other.
The number of transects in each patch was 6, but they varied in length depending on the size of
the patch. While walking along each transect, all plants to the species level were recorded 1
meter on the left side of the transection until the entire patch was accounted for. This was
repeated for the entire prairie patch and yielded an accurate collection of the plant species
present in the Science Hall Prairie and their abundance. Plant species that were not able to be
identified in the prairie were collected and numbered in zip-lock bags. These unknown plants
were then taken to the lab and identified used lab manuals or web databases. The plant diversity
was obtained three separate times: two plots were surveyed in early October 2013, three plots
were surveyed towards the end of May 2014, and all five plots were surveyed in mid-August
2014. The final survey was done of all five prairie plots, and it was done during the peak of the
season, so it will be the primary focus for statistical analysis and further discussion.
Pollination
The second phase of this research included examining the pollinators and their
effectiveness through seed set and viability. Two plants that had a moderate abundance in the
prairie were examined for pollination. The plant more extensively examined for pollination was
Echinacea purpurea (Purple Coneflower), and the plant that was examined more in regards to
seed set and viability was Rudbeckia subtomentosa (Sweet Black-eyed Susan).
In total, nine Purple Coneflower plants were used in the pollination aspect. These plants
are referred to patches throughout the study due to their abundance of flower heads that were
observed for pollinator foraging and treated with the two pollination mechanisms. For an
approximate composite two hours, four of the Purple Coneflower patches were observed for
pollinator activity or natural pollination. This was simply done by watching the flower patches
for what pollinators visited the flowers and recording how long the pollinator would spend on
each flower before moving to the next one until it eventually flew away from the patch. In
contrast to this, there were six Purple Coneflowers from the specified patches, which were
control groups and used for self-pollination. The self-pollination of the six flowers was done
manually by tying cheesecloth around the flower’s head and petals just before the disk florets
opened up and began producing pollen. With these flowers being bagged, there was no way for
pollinators to transfer any pollen to and from these control flowers. At two different points, once
the flowers began to produce pollen, the bags were temporarily removed from the flowers and a
fine paint brush was used to brush the pollen into a petri dish. This pollen was then manually
used to pollinate another bagged flower from a different plant. After the pollination of the
flowers was complete, the bags were then securely returned to the flowers to prevent any natural
pollination. At the point when it was determined that the flowers had completely opened up and
no more pollen was being produced by the flower, the bags were removed.
A very similar process was done from the Sweet Black-eyed Susan, except for the
pollinator observations. Six patches that contained plants with an abundant amount of flower
heads were marked for observations. Five of these patches contained bagged flowers that were
the control and used for self-pollination. In total there were eight Black-eyed Susan flowers that
were bagged and self-pollinated using the same methodology as the Purple Coneflowers.
Seed Viability
The first step in checking for seed viability was to collect dried flower heads of both
species. When the flower heads were observed to be completely dry and the sepals were no
longer green, all of the bagged flowers of both species were collected. In addition, twenty Purple
Coneflowers were collected and eight Sweet Black-Eyed Susans were collected. Each of these
dried flower heads was taken apart and the seeds were separated from the other flower parts and
then counted in order to determine seed set
After the seed set was calculated for each collected flower, a smaller sample size was
used for the cold stratification. Eight of the randomly selected Purple Coneflower and Sweet
Black-eyed Susan were used for the cold stratification, as well as all of the bagged flowers from
both of the species. The cold stratification was completed by placing a filter paper moistened
with distilled water in a sterilized petri dish and then placing between 10 and 15 of the flower’s
seeds onto the filter paper. The seeds were spread out a sufficient distance so that they were not
touching, thus decreasing the chances of mold infestation. Another moistened filter paper was
then placed on top of the seeds, and the lid of the petri dish was intact. Two layers of aluminum
foil were wrapped around the petri dishes in order to simulate complete darkness. The petri
dishes were stored at 5⁰ C for 21 days. A previous study by Fariman, et al. (2011) indicated that
cold stratification for 21 days at 5⁰ C was the ideal condition for the highest germination
percentage and rate for seeds. After this period of time the seeds were then germinated.
Germination
Of the seeds that underwent cold stratification, only the ones that appeared to have no
mold infestation were used for germination. In a sanitized area, the seeds were transferred into a
clean petri dish with filter paper moistened with distilled water. The petri dishes were labeled
and wrapped with two layers of aluminum foil to simulate complete darkness. The wrapped petri
dishes were then placed in an incubator set to 27 ⁰C, mimicking a constant room temperature.
The petri dishes with seeds were checked every few days for 3 weeks to observe any germination
or mold infestation and to remoisten the filter paper. Germinated seeds were recorded and
removed from the petri dishes, while seeds that exhibited mold were discarded and removed
from the germination percentage data.
Results
Diversity
The first result that was found from the research was an estimate of species richness in
the Science Hall Prairie. Table 1 shows the variations in species richness depending on the
season, and there is a separation between
Table 1. Estimates of Species Richness in the
Science Hall Prairie
Parameter
Fall
2013
Spring
2014
Summer
2014
grasses and forbs (non-grasses). The total
Species richness (total
number of species
22
43
34
estimate of species present in the prairie
Number of species of
forbs
20
37
30
was 62. This is including the species that
Number of species of
grasses
2
6
4
were unable to be identified due to the
lack of flowering fruits. Additional
results from the plant diversity are present in the appendix seen in Table 2. This appendix gives
the scientific names of all the plants in the prairie, excluding the plants that were not identified.
The appendix is separated by seasons in order to show when the given plants were identified in
the prairie.
Table 2. Appendix of Plant Species found in Prairie
Taxon
Poaceae (grasses)
Andropogon geradii
Sorghastrum nutans
Sporobolus heteroleois
Elymus virgincus
Elymus canadensis
Panicum anceps
Fall 2013
Spring 2014
Summer 2014
X
X
X
X
X
X
X
X
X
Bromus kalmii
Koleleria macrantha
Asteraceae (sunflowers)
Echinacea purpurea
Ratibida pinnata
Erigeron annuus
Silphium perfoliatum
Silphium laciniatum
Rudbeckia hirta
Liatrus espera
Silybum marianum
Solidago sp.
Aster sp.
Eryngium yuccifolium
Eupatorium serotinum
Heliopsis helianthoides
Helianthus mollis
Parthenium integrifolium
Rudbeckia subtomentosa
Rudbeckia laciniata
Echinacea pallida
Coreopsis lanceolata
Vernonia sp.
Silphium integrifolium
Nothocalais cuspidata
Eupatorium serotinum
Urticaceae (nettle)
Urtica sp.
Lamiaceae (mint)
Monarada fistulosa
Teucrium canadense
Glechoma hederacea
Fabaceae (legume)
Baptisia australis
Amorpha canescens
Astragalus adsurgens
Apiaceae (carrot)
Daucus carota
Polytaenia nuttallii
Campanulaceae (bellflower)
Lobelia siphilitica
Onagraceae (evening-primrose)
Gaura parviflora
Gentianaceae (gentian)
Gentiana puberulenta
Verbanaceae (vervain)
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Verbena stricta
Asclepiadaceae (milkweed)
Asclepias sp.
Bassicaceae (mustard)
Alliaria petiolata
Anacardiaceae (cashew)
Toxicodendron radicans
Commelinaceae (spiderwort)
Tradescantia sp.
Scrophulariaceae (figwort)
Penstemon palidus
Rubiaceae (madder)
Galium borerale
Polygonacea (buckwheat)
Polygonum arenastrum
Violaceae (viola)
Viola sp.
Liliaceae (lilium)
Lilium sp.
X
X
X
X
X
X
X
X
X
X
X
Seed Production
The outcomes from computing seed-set of the two focal prairie plants, Purple Coneflower
and Sweet Black-Eyed Susan, are seen in Figure 1. This table shows the average seeds produced
by both of the plants under each pollination treatment. For Purple Coneflower there was no
significant difference (p-value=0.217) between the hand and naturally pollinated flowers. For
Sweet Black-Eyed Susan, the naturally pollinated flowers produced a significantly higher
amount of seeds when compared
to the hand pollinated flowers (pvalue<0.01). This graph along
with Figure 2, suggests an
interaction effect where the two
species do not respond the same
way to the two treatments. The seed production between the two species was not consistent
between the two methods of pollination. Although for Purple Coneflower there was not much of
a difference between the two treatments, Sweet Black-Eyed Susan showed a much greater seed
production when
pollinated naturally as
opposed to hand
pollination.
Germination
To assess the
viability of the seeds
from the two types of flowers the seeds were germinated. Overall, the amount of seeds that
germinated for both of the flowers and both of the treatments was lower than the amount of seeds
that did not germinate. Figure 3
shows the percent of seeds that
did and did not germinate for
each flower. This graph does
not take into account the
differences that occurred
dependent on the type of
pollination treatment. A
significant difference for both plants occurred implying that under the null hypothesis there were
a higher percentage of seeds that were expected to germinate. The data was run under loglinear
statistical analysis since the response variable was binary as opposed to qualitative. Although for
all groups a low amount of seeds germinated, it can also be seen in Figure 3 that significantly
more seeds germinated for Purple Coneflower than for Sweet Black-Eyed Susan (p-value=
0.001). Between hand and natural pollination there was no significant difference in the amount of
seeds that germinated (p-value= 0.276). The last piece of significant data indicated that there was
not a consistent response between the two species in regards to pollination method. A
significantly higher percentage of hand pollinated Purple Coneflower seeds germinated (44.6%)
when compared
to the
percentage of
hand pollinated
Sweet BlackEyed Susan
seeds that
germinated which was only 3.8% (p-value= 0.013). This is seen in Figure 4, where the percent
germination for the Purple Coneflower under the hand pollinated treatment was much higher
than any of the other treatment and species factors.
References
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world crops. Proc. R. Soc. B 7 February 2007 vol. 274 no. 1608 303-313.
Solomon, M.E. (1971). Review of J. B. Free 'Insect Pollination of Crops' Experimental
Agriculture, 7, pp 367-368. doi:10.1017/S0014479700023401.
URL 1. Pollinator Partnership. https://pollinator.org/pollination.htm
URL 2. “Factors Affecting Bee Pollination of Tree Fruits”. Washington State University.
https://das.wsu.edu/news/story/2013/03/29/Factors_Affecting_Bee_Pollination_of_Tree_
Fruits
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digitalis (Plantaginaceae), with multiple pollinators. American J of Botany. 2007: 94(10):
1594-1602.