Invasion by Lonicera japonica Impacts Species Turnover in a Successional System

Kathryn A. Yurkonis and Scott J. Meiners
Department of Biological Sciences, Eastern Illinois University.

Introduction

Community diversity often decreases with exotic species invasion. However, the mechanisms of this reduction are poorly understood. Diversity results from a balance between species colonization and extinction within communities. To change species richness, an invader must alter the balance between colonization and extinction rates within a community.

We used data from a long term Buell-Small Succession Study (BSS) in the William Hutcheson Memorial Forest (Figure 1) to evaluate the impact of Lonicera japonica invasion on community dynamics at 3 levels:

1. Species richness
2. Species turnover
3. Individual species colonization

Figure 1. William Hutcheson Memorial Forest.

The long term study area includes ten fields abandoned from agriculture beginning in 1958 (Figures 2 and 3).  Vegetation dynamics have been followed in forty eight permanently marked 0.5 x 2.0 m plots in each field.  For more information, visit the Buell-Small Succession Study web site at http://www.ecostudies.org/bss/

	Figure 2.  BSS successional field ten years after abandonment.
	Figure 3. L. japonica entwining Solidago rugosa.

Methods

We used BSS permanent plot data to examine changes from the beginning (T1) to peak (T2) of

L. japonica invasion (Figure 4).
 

For each plot we quantified:
    - Change in L. japonica cover.
    - Change in species richness.
    - Number of local species gained-species colonization.
    - Number of local species lost-species extinction.
    - Colonization dynamics of common invaders.

Results

Each point represents the colonization rate of the indicated species based on presence/absence data over ten percent increments of change in L. japonica cover.

1. As L. japonica invades, species richness declines (Figure 5).

2a. As L. japonica cover increases, rate of species colonization decreases (Figure 6).

2b. As L. japonica cover increases, rate of species extinction stays constant (Figure 7).

3a. L. japonica invasion decreases the probability of select native species colonization (Figure 8).  Additional species negatively affected by Lonicera invasion include: Achillea millefolium**, Solidago rugosa**, Aster pilosus* and Euthamia graminifolia*. ** P <0.01 * P < 0.05

3b. In some cases, L. japonica has no impact on native colonizing species (Figure 9). Additional common colonizing species not affected by Lonicera invasion include Solidago juncea, Parthenocissus quinquefolia and Toxicodendron radicans.

3c. L. japonica shows mixed impacts on other invading exotic species (Figure 10). While Lonicera invasion inhibits Rosa multiflora invasion, Lonicera shows no impact on the exotic invaders Poa compressa, Daucus carota and Hieracium caesptiosum.

Figure 5.	Figure 6.	Figure 7.
Figure 8.	Figure 9.	Figure 10.

Conclusions

1. Invasion of L. japonica causes a decline in species richness.
2. Lonicera invasion inhibits species colonization without impacting species extinction rates.
3. Lonicera differentially impacts common colonizing species.

These findings contradict the traditional competitive exclusion view where species extinctions are the primary mechanism for declines in species richness.  Instead, these data suggest that preemptive competition by exotic species reduces local colonization rates causing declines in species richness.

Acknowledgements

Funded by the Council on Faculty Research and EIU College of Sciences Graduate School.