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.

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