BIOL 475 Lab 2: Alien Weeds and the Bees Who Love Them.

Detecting competition between native and non-native plants for pollinators in Liberty State Park.

Goals

1 Observe and compare bee visitation rates at a native (Goldenrod, Solidago canidensis and non-native (Purple Loosestrife, Lythrum salicaria) flowering plant.

2 Compare the gross diversity of bee visitors to native and non-native flowering plants.

3 Quantitatively compare the diversity of bees collected via netting at patches of Goldenrod and Purple Loosestrife.

4. Practice field techniques including timed observations and sweep netting.

5 Practice preparing bee specimens in the lab and grouping bees into morphotypes.

Introduction

An invasive species is a species that does not naturally occur in a specific area and whose introduction does or is likely to cause economic or environmental harm or harm to human

health. Typically, we don not refer to a species as invasive until it has become established in its new habitat and is increasing in abundance. Many species are moved around the globe accidentally (or on purpose) by human activities, and yet only a tiny fraction thrive in their new environment. In those rare cases where the introduced species finds itself in an environment that meets all of its basic needs, it can often grow unchecked as it is released from the pressure of predators or parasites that occur in its native range.

Invasive plants are of particular concern because they are capable of changing the basic structure and thereby function of native ecosystems by competing with and replacing native plant species. Non-native plants can change community composition sufficiently to permanently change the dynamics of a landscape, favoring different sets of species and possibly interfering with the ecosystem services on which humans depend. These changes include increased sedimentation, increased evapotranspiration, increased nitrogen fixation, changes in native fire regimes, etc. Changes in community composition can lead to the decline of native plants through a variety of mechanisms (Mack et al 2000). The prevention of recruitment (the establishment of new individuals) of plant species by non-natives is of concern because the loss of native plant diversity may be detrimental to the biota that depend upon the resources provided by the native community (Blossey 1999).

Prevention of recruitment of native plant species by non-native plants may occur because specific non-natives may be better at competing for resources. This has been documented to be more prevalent in disturbed areas, where populations of native species may be under stress due to lack of ideal conditions and the presence of predators. The means of competition vary in mechanism and include competition for pollination services (Campbell 1985, Goodell 2008).

The use of pollinators by non-native plant species can lead to reduced seed set for native plants. When a pollinator visits one plant right before one of a different species, it will bring the incompatible pollen to the second plant which has been observed to reduce seed set in comparison to plants visited by a pollinator that has just been at a plant of the same species — this is sometimes referred to as a dilution effect (Brown 2001, Campbell and Motten 1985). Additionally, invasive plants have been recorded as attracting significantly more pollinator visits in comparison to native plants (Bartomeus et al 2008, Lopezaraiza-Mikel et al 2007).

Recent declines in North American native pollinators could potentially be attributable to changes in plant communities and the growing prevalence of non-native species. The floral bloom of native plant species coincides with a coevolved system of plants and pollinators (Campbell 1985). While pollinator species richness on native vs. invasive plants has been recorded as similar, the actual identity of the specific pollinators may be quite different with invasive species attracting generalist pollinators. This leaves specialist pollinators with fewer resources as the plants they specialize on are out competed. (Allen-Wardell et al 1998, Bartomeus et al 2008).

In order to assess the degree of overlap and/or competition for pollinators, we will examine the bee communities associated with one native and one non-native flowering plant of roughly equal abundance in the disturbed habitat of Liberty State Park, NJ.

The Players

Purple loosestrife, Lythrum salicaria. Purple loosestrife was accidentally and deliberately introduced to North America in 1814. Its seeds may have been carried in ship ballast or on the coats of imported animals. Immigrants brought the plant for its medicinal value. Recently, purple loosestrife has been planted for honey production and ornamental purposes. While loosestrife populations are especially concentrated in the Northeast, purple loosestrife occurs in every U.S. State except Florida. It is also found in Ontario, Québec, the Maritime Provinces, and British Columbia. It is regarded as such a serious problem that it is illegal to sell this plant in some states. Its ability to produce 120,000 seeds per flower head and almost three million seeds per plant — achieved by a long flowering season — makes purple loosestrife a formidable invasive, indeed! The small seeds have an 80% survival rate after 2 years of dormancy, establishing a large long-lived seed bank. Seeds are also dispersed by birds and waterways. Additionally, the plant forms adventitious roots and shoots from damaged or buried stems. Because North American predators are few and because of its highly efficient means of reproduction, purple loosestrife has colonized disturbed wetland areas quickly. It out-competes even robust species such as cattail, and reduces the quality of wetland habitats for wildlife dependent on cattail for food and shelter, such as muskrats, marsh wrens, and swamp sparrows. Foraging by deer is insufficient to damage the loosestrife and actually promotes the growth of additional stems (text from http://www.nywea.org/clearwaters/pre02fall/311040.html)

Goldenrod, Solidago canidensis. About 100 perennial species make up the genus Solidago, most being found in the meadows and pastures, along roads, ditches and waste areas in North America. This many-rooted rhizome grows to a height of about 30 inches. The leaves at the base of the plant are bright green and pointed ovals, while the leaves on the flower stem are smaller ovals. The flower stems produce spikes of simple golden yellow flowers, which have clusters of stamens. Goldenrod pollen is too heavy and sticky to be blown far from the flowers, and is thus mainly pollinated by insects. Propagation is by wind-disseminated seed or by underground rhizomes. They form patches that are actually vegetative clones of a single plant.

The Place

Procedures

We will travel by van to Liberty State Park, NJ. We will locate two established patches of purple loosestrife and two established patches of goldenrod. At each location we will

1. Mark off 4, 1m² plots surrounding dense patches of flowers using flagging, separated by a minimum of 1 meter.

2. Working in groups of 3, each group will observe 1 square for 15 minutes. Each student in the group will do 5 minutes of observation. All visits by bees will be recorded and classified based on size and color.

3. When all groups have finished their observations, students will spend approximately 15 minutes netting as many bees as possible in the floral patch. Bees will be preserved in killing jars and taken back to the lab for further identification.

These three steps will be repeated at each of the four study sites.

Assignment.

1. Each group will enter their data in a spreadsheet and e-mail/upload it by Wednesday the 23rd. Be sure to include the names of everyone in your group!

2. Based on their own observations, every student should answer the following questions and e-mail/upload their answers by Wednesday the 23th.

a. At which site did you observe the most number of bees?

b. At which site did you observe the most diverse community of bees?

c. Do you think any differences you observed between sites can be best explained by the plant species (native/non-native)? Why or why not?

d. Can you think of any reason why individual bees might prefer one plant over the other, regardless of its native/non-native status?

e. Can you suggest any modification to the methods we used that would better allow us to make comparisons of the pollinator communities of native and non-native plants?

Quantitative analyses will be performed by those individuals assigned to write up a formal report for this project. Details to follow.