Insect biodiversity in relation to plant diversity and soil factors for a planted flower garden at
Gorgas Park, Philadelphia, PA, USA
Katharine Novak, Patrick Aberin, Nicole Epting, and Jenna Scurti
Dr. Bower
Ecology
1) INTRODUCTION:
It is important to understand the relationship between soils, plants, and insects because
they make up a good amount of our Earth’s biodiversity. Plants are important to our planet
because they help keep our environment healthy in a number of ways. Plants are able to convert
light energy from the sun initially providing the food we eat. (Missouri Botanical Garden, 2009)
Plants are able to make oxygen gas which is an important aspect of life as it helps us humans and
animals breathe. (Missouri Botanical Garden, 2009) The roots of a plant help hold soil together
which helps reduce erosion and conserve the soil. Since soil is made up of particles of rocks that
are broken down into small pieces, the decomposed remains of plants when they die help keep
the soil rich with nutrients. (Missouri Botanical Garden, 2009)
Many people might be disgusted by the sight of insects but in reality, they are an
important part of life. Insects help pollinate many of the fruits and vegetables we eat. They have
a very important role acting as primary or secondary decomposers. If insects are not able to
break down and dispose of the wastes of dead animals and plants, then our environment would
accumulate all those rotting carcasses. (Gibb, 2009)
Pollinators are an important aspect in agriculture. Animal pollinators are known for
producing more than one-third of our food products. The most well-known pollinator would be
the bee. Bee pollination commodities accounts for about $20 billion in annual U.S agricultural
production and $217 worldwide. (Farm Service Agency, 2013)
Insects have been widely used as alternative medicine for many years. Promising
treatments have been studied experimentally and certain results were found that help cure
ailments people experience. Maggots and honey have been used to help treat chronic and post-
surgical wounds. The honey of the bee has been combined with beeswax to help treat several
dermatologic disorders such as atopic dermatitis and pityriasis versicolor. (The Geriatrics
Institute, 2010) Bee and ant venom have reduced the number of swollen joints with rheumatoid
arthritis. (The Geriatrics Institute, 2010)
According to the Insect Identification organization, there are a total of 277 different
species of bugs found in Philadelphia as of February 25, 2014. It does not say the particulars on
the dominant taxa, but a few of species to name off include the American cockroach (Periplaneta
Americana), American dog tick (Dermacentor variabilis), American house spider (Parasteatoda
tepidariorum), Eastern amberwing (Perithermis tenera), and the field cricket (Gryllinae).
(Insect Identification Organization, 2014)
According to Rawlins & Beir, there are a total of 11,702 species in Pennsylvania where
282 of the species are of special concern, 37 considered extirpated, and 38 are only known from
historical records. (Rawlins & Beir, 2005) Below is a chart of the total number of species of
organisms in Pennsylvania:
Fig. 1. Species diversity of the major groups of organism in the Pennsylvania biota.
This figure is based on an estimated 21,884 species of organisms in Pennsylvania.
(Rawlins & Beir, 2005)
Below is a chart showing the percentage of Pennsylvania invertebrates that are of special
concern:
Fig. 2. Conservation status of Pennsylvania invertebrates of special concern
as registered in the Pennsylvania Natural Diversity inventory (PNDI).
This figure is based on 282 species of special concern as of July, 1998.
(Rawlins & Beir, 2005)
According to the UGA Center for Invasive Species and Ecosystem Health, there are a
total of 668 invasive species reported and a total of 38,356 records from all the plants ranging
from aquatic, vines, shrub, hardwood trees, grass, forbs/herbs, and conifer trees. (UGA Center
for Invasive Species and Ecosystem Health, 2014) The top ten abundant invasive plants in order
are the Japanese stillgrass (Microstegium vimineum), spiny plumeless thistle (Carduus
acanthoides), multiflora rose (Rosa multiflora), musk thistle (Carduus nutans), Japanese
barberry (Berberis thunbergii), garlic mustard (Alliaria petiolata), Japanese honeysuckle
(Lonicera japonica), watercress (Nasturtium officinale), oriental bittersweet (Celastrus
orbiculatus), and wineberry (Rubus phoenicolasius). (UGA Center for Invasive Species and
Ecosystem Health, 2014)
According to Science Summary, the number of pollinators is declining due to a number
of reasons. Habitat loss, fragmentation and modification are two reasons for the decline. Habitat
loss negatively affects the timing and amount of food availability which increases the
competition for limited resources. (Science Summary, 2008) The World Conservation Union
predicts that at least 20,000 flowering plant species will be gone in the next week decades.
(Science Summary, 2008) Pollination activity is disrupted by other introduced insects and
mammals. (Science Summary, 2008)
2) METHODS:
The site that our group sampled from was the garden. The garden had a variety of plant
life some invasive, and some not. There were two separate gardens in close proximity, and three
Pitfall Traps placed in them. The plant life in a garden is more fragile and well-kept than a spot
in the woods, so we had to be more delicate with our methods than the other groups. Out of the
five methods introduced to us, we only used two, which were Pitfall Traps, and Sweep Netting.
Pitfall Traps:
These traps are generally used for vegetation that grows low to the ground, which was
exactly what this garden was made up of. The trap is a container or plastic cup, basically set or
sunk in the ground and filled with a preservative. It works simply by having the insects fall into
the container and the preservative keeps them from leaving before being able to be observed. The
preservatives are beneficial because it can prevent them from being preyed on and also decaying.
Some Pitfall Traps are baited, which means the preservative inside the container attracts the
insects, such as using agave nectar. On our site, there were 2 unbaited (olive oil) Pitfall Traps,
and 1 baited (agave nectar). After having our Pitfall Traps sit overnight, we poured them out onto
petri dishes and observed and identified our findings.
Sweep Netting:
Sweep Netting is also a method that is used for vegetation that grows low to the ground,
which again, was exactly what kind of plant life the garden was made up of. To perform this
method, the sweep net is passed deeply along the vegetation in backhand and forehand strokes.
This is lightly done though, unlike beating, which can harm plant life in some cases. This garden
was very well preserved so the sweep netting technique was utilized to observe and identify
insect life, while keeping the plant life intact.
The next three methods were learned, but not utilized in the garden section.
Beating:
The beating method is similar to the Sweep Net, but much more aggressive. With
beating, the net or stick is hit very powerfully against the plant or branches to disturb
invertebrates and have them fall into this net or onto a tray being held under the stick. Beating
can get very good results and a large variety of species, but it can also be detrimental to fragile
plant life.
Light Trap:
This trap is designed around the fact that many different insects are attracted to light, and
make their way towards them. This trap contains a UV light and a funnel that has the insects fall
into the trap towards the light, and they are unable to escape. This trap will not catch a huge
variety of invertebrates due to the fact that it is veered towards those who are attracted to the
light.
Quadrat Sampling:
Quadrat sampling is a method that Ecologists use to collect a sample of an environments
species without having to sample a very large area. The Quadrat is a large rectangle with a grid
inside, made up of wire. This method is good for estimating the abundance and density of plants
in one area. The size of the Quadrat has a large range, depending on the size of the sample
needed. When using Quadrat sampling, errors can easily occur such as measurement errors, and
the assumption of the population dispersal. It is also important to not sample a bias area when
using Quadrats, such as sampling near a path where vegetation may be more scarce than other
areas.
3) RESULTS:
The biotic factors found in the garden sites at Gorgas Park were plants and insects. The
plants found between the three sites were Aster, Sedum, Echinacea, Yellow Native Sunflower,
Milkweed, Salvia nemerosa, White Daisy, Tall Purple Weed, Canna Lily, and a Japanese
Horticultural Shrub. The insects found between the three sites were general Bees, Spiders
(Brown Recluse and Daddy Long Legs), Ants, European Mantis, European Earwig, Grasshopper,
Mayfly, Armadillidiidae, and unknown species. All three of the garden sites lacked shade from
nearby trees, meaning that the sites have unlimited sunlight during the daytime.
Fig. 3: A comparison of the abiotic factors (wind speed, soil pH, and soil humidity) that
were consistently measured at all three Gorgas Park garden sites.
Below are photographs taken of most of the plant—and some of the insect—species that
were found at the garden sites:
Yellow Native Sunflower (Helianthus annuus): Yellow petals with a dark brown flower; pointed
leaves that come out from stem at the same location
White Daisy (Leucanthemum vulgare): White or purple (mature) petals with yellow flowers
Sage (Salvia nemerosa): Maroon stalks and flowers
Milkweed, or butterfly flower (Asclepias syriaca) : Green stalks with brown-pink flowers
Echinacea (Echinacea purpurea): Although the petals have already fallen off for the year, they
are usually a bright pink; black, spiky seeds centrally located
Canna Lily (Canna generalis): Green stalks with consistent leaves, vibrant red petals
Aster (Aster amellus): Purple petals, arranged as a shrub
Grasshopper (Schistocerca americana): Antennae, arrowhead detail in the hind legs, white spots
with black in the middle immediately behind the head
European Mantis (Mantis religiosa): Bulbous end section, colored pincers, brown design in rear
section, distinctive white spot with black in the middle on the forearms right before the body
Fig. 4: A pie chart displaying the petal color of the plants that were found in the Garden area
Fig. 5: A pie chart displaying different types of diet and how many of each of the found insect
species follows which diet
1
2
2
1
2
1
Purple
Green
Pink
Yellow
Red
White
2
2
1
2
1
Herbivore
Carnivore
Omnivore
Detritivore
None
Fig. 6: The above chart shows how many insects from each of the identification groups were
found within the three Garden sites at Gorgas Park.
The above charts demonstrate the flower color of the plants, the diets of the insects
found, and how many of each type of insect were found there. The three types of insects that
were found the most were Bees, Spiders, and Ants. Bees live off of the pollen and nectar of the
flowers in the garden, thus creating a healthy mutually-shared relationship. Ants have a non-
specific diet that ranges from flower pollen to other insects, thus they can easily live off of all the
resources found within this garden. The spiders are carnivores: they prey upon other insects
found in the garden. These three types of insects clearly demonstrate the cyclical pattern of the
life cycle in this small area, and their numbers also demonstrate that this environment is effective
even though the area is small.
0
2
4
6
8
10
12
14
16
# Insects
Aster: Native; Sedum: Native; Echinacea: Native; Yellow Native Sunflower: Native;
Milkweed: Native; Salvia nemerosa: Native; White Daisy: Native; Tall Purple Weed: Native;
Canna Lily: Native; and Japanese Horticultural Shrub: Unknown.
Most of the insect species are in their preferred habitats. Although the insect diets range
from herbivore to detritivore to carnivore, the small ecosystem is able to provide for them: the
herbivores are able to live off the plant life, the detritivores can survive on whatever dead matter
can be found, and the carnivores feed on the other insects in the garden. Most of the plant
species thrive in this environment; however, some such as the Sedum prefer to be less clumped
together in order to thicken. (United States Department of Agriculture)
The dominant plant species were the Aster, White Daisy, and Japanese Horticultural
Shrub. The dominant insect species were general Bees, Ants, and Spiders. The European
Mantis, Mayfly, Grasshopper, and European Earwig were rare within this area.
The soil pH stayed relatively consistent, which makes it reliable for any existing plant
and animal life. The pH is also neutral to slightly basic, which means that there are several other
species of plants and animals that could easily be introduced into this area. The soil moisture
only varied by ten percent between the three sites, which makes it stable; however, the moisture
was relatively low- 25-35% humidity. Perhaps the area needs to be watered on a more regular
basis, or perhaps the temperature that day had dried up a lot of the water there. Overall, this area
seems to be stable and thus reliable for the existing plant life, which means that it would be a
good time to introduce more diversity; however, the given garden area is small (29 steps by 11
steps), thus the garden would have to be expanded before introducing more diversity.
4) DISCUSSION
The soil pH was very close or exactly 7 at all three sites, which is good because most
plants prefer a neutral pH. The soil of moisture at Aster was 25%. The soil moisture at Daisy was
35% and the soil moisture at Japanese was 30%. The plants listed from Aster were: Echninacea,
Aster, Sedum, Yellow Native Sunflower, and Milkweed. These plants are all native to the area of
Pennsylvania. For the Daisy section the plants found there were: white daisy, tall purple weed,
and canna. The only native plant is the tall purple weed. For the Japanese section a Japanese
Horticultural Shrub was listed. The Aster site had the most diversity, including: several bees,
spiders such as 3 Daddy long legs, 5 ants, 1 European Mantis, and 1 European Earwig. At the
Daisy site there were 1 grasshopper, 4 ants, 1 mayfly, 2 Armadillidiidae, and 1 spider. Lastly, at
the Japanese site, there were 3 spiders, including: 2 Brown Recluses and one other unidentified
spider, 2 Armadillidiidae, and 6 ants. The relationship shows that because the pH of the soil was
neutral, there was enough moisture for the soil, which allows the plants to grow well and creates
diversity within the field. The more plant diversity, the more biodiversity it will create, such as
an increase in the amount of insects.
It shows that the more plant life there is, the more biodiversity there will be. (NYTimes,
2014) Although in the article from the New York Times, Mary Myers displayed a larger more
diverse garden than Gorgas Park. It shows that if Gorgas Park increases the garden amount the
biodiversity will increase as well providing a direct relationship.
It was surprising to find such a diversity of insects in that small of an area. It was unusual
finding a praying mantis in the area. Since the soil pH was neutral, it could maintain plant life
and therefore support a diverse insect life.
5) CONCLUSION
We have noticed that the garden at Gorgas Park was expanded which caused the great
diversity it has. To further increase the diversity of the garden it would be recommended to keep
expanding the garden spaces and to provide more native diversity as well as non-natives. This
has been done in Wyncote, PA by Mary Myers, a landscape architect and professor from Temple
University. She created a 200 ft. rain garden beside her sloped lawn in downtown Philadelphia.
She increased the biodiversity while still making it appealing to viewers. One plant she had was
the blue mistflowers, which viewers thought were beautiful. The wind carries the seeds around
the neighborhood, which creates more biodiversity indirectly. An interesting tactic she had was
calculating a depth for absorption in rain, because she agreed with scientists that climate change
will bring a 20% increase of rainfall in the Northeast (Raver, 2014). Other appealing and diverse
natives that can be included at Gorgas Park can be: Helenium autumnale, which is also known as
the common sneezeweed that blooms in the late summer or fall, the Liatris spicata also known as
the blazing star, and the Solidago genus also known as the golden rod. Gorgas Park has an area
along the side with a more expansive garden; if this is done to the front garden, it will drastically
increase the amount of insect and plant diversity, creating rich wildlife throughout the park.
References
(2014). Plants profile for Hylotelephium erythrostictum (garden stonecrop). United States
Department of Agriculture.
The Geriatrics Institute, University of Miami Miller School of Medicine. (2010, July 15). Bugs
as drugs, Part 1: Insects: The "new" alternative medicine for the 21st century? Retrieved
from http://www.ncbi.nlm.nih.gov/pubmed/20806997
Gibb, T. (2009). Who let the bugs out? | Purdue | entomology | insect | collect | supplies |
specimen | mounting | identifying | displaying | preserve | labels. Retrieved from
http://extension.entm.purdue.edu/radicalbugs/default.php?page=importance_of_insects
Farm Service Agency. (2013). Pollinators. Retrieved from
http://www.fsa.usda.gov/FSA/webapp?area=home&subject=ecpa&topic=nra-pl
Insect Identification Organization. (2014, February 25). pennsylvania insects and Bugs.
Retrieved from http://www.insectidentification.org/insects-by-
state.asp?thisState=Pennsylvania
Missouri Botanical Garden. (2009). Biology of plants: plants and life on earth. Retrieved from
http://www.mbgnet.net/bioplants/earth.html
Raver, Anne. "One Woman’s Pipe Dream." The New York Times. The New York Times, 08
Oct. 2014. Web. 13 Oct. 2014.
Science Summary. (2008). CES - pollination tool Kit: pollinators in decline. Retrieved from
http://www.esa.org/ecoservices/poll/body.poll.scie.decl.html