Species Richness in Space and Time

Bill Lauenroth, Peter Adler, and Ethan White

Activities

Our workshop at the LTER-ASM had three objectives: 1) Present recent research on species-time and –area relationships, 2) evaluate interest in and possibilities for further cross-site synthesis using LTER data, and 3) discuss new data collection programs for LTER that could fill existing gaps in knowledge.

The workshop began with four presentations (Objective 1). Peter Adler presented results from a paper recently published in Ecology Letters showing that species accumulate very rapidly through time on small plots (1-10 m²) in grassland communities at Hays, KS and Konza Prairie. These species-time relationships (STRs) were well-fit by the power-law function typically used for species-area relationships (SARs). However, the slopes of these relationships, a measure of species turnover through time, were very steep compared to the slopes of SARs from the same sites. The slope of the STR decreased as the spatial scale of observation increased—species turnover slowed as spatial scale increased. Nevertheless, time had a strong effect on species number even at scales too broad to be directly sampled.

Ethan White, showed a method to partition STRs into a sampling phase and an ecological change phase, illustrated with data from the Breeding Bird Survey. This method will be critical for comparison of STRs across sites and taxonomic groups, since the importance of sampling effects may vary dramatically. He also showed that because of differences among sites in the STR, pairwise comparisons of richness often yield different results when evaluated using 1 year compared to 10 years of data, a result with important implications for biodiversity assessment and conservation planning.

Jin Yao, the third speaker, presented vascular plant data from the Jornada site that supported Adler’s findings of very rapid species turnover in time. In fact, the Jornada STRs had steeper slopes than those from Hays despite a smaller observed species pool. The steep slopes of these STRs may be related to the shift from grass to shrub dominance during the period of record on many of these quadrats.

Tim Kratz ended the formal presentation portion of the workshop by broadening our perspective with data on fish communities in the Northern Temperate Lakes system. Although his analyses were preliminary, they showed influences of time on species number, and interactions with lake size (spatial scale) that appear consistent with Adler’s results. Most importantly, this presentation demonstrated that appropriate datasets from a wide variety of ecosystems exist.

After these talks, the discussion of a potential cross-site synthesis (Objective 2) proceeded for well over an hour. Overall, the workshop participants felt that this topic is important and interesting and deserves further treatment. A number of participants offered to contribute suitable datasets. Additional participants expressed interest in working on a synthesis product. Given the in-depth discussion about synthesis, we decided to leave discussion of LTER data collection activities (Objective 3) for the future.

Accomplishments

Since the workshop, we have focused on defining general and specific objectives for the synthesis activities and have also begun collecting datasets for analysis. Our primary objective is to write a manuscript to be submitted to a journal, perhaps Ecology that synthesizes what we know from available datasets about the STR, the SAR, and the STR-SAR interaction.  A secondary objective is to write a manuscript, or perhaps several, that discuss the consequences of the STR and STR-SAR interaction for particular disciplines such as conservation biologists, theoretical and empirical ecologists, and natural resource managers.

Our specific objectives fall into two categories, data analysis and inference. The data analysis objectives are a) Test whether the STR is as general a pattern as the SAR; b) Test whether the slope of the STR is variable across sites and taxonomic groups; c) Test whether the relationship between the intercept of the STR and mean species richness is the same across sites and taxonomic groups; d) For those sites with temporal and spatial data, test whether the interaction term in the species-area-time relationship varies with ecosystem type (site).

The inferential objectives are a) Evaluate the consequences of the STR and STR-SAR interaction for decisions about the location and size of biodiversity reserves (target audience Conservation Biologists); b)  Evaluate the consequences of the STR and STR-SAR interaction for ecological modeling and data collection (target audience Empirical and Theoretical Ecologists); c) Evaluate the consequences of the STR and STR-SAR interaction for management decisions related to sustaining biological diversity (target audience Natural Resource Managers).

We have agreed on a standard data format and have begun acquiring data for analysis. Below is a preliminary list of data sources:

Site	Contact	Taxa	Years
Hays	P. Adler	plants	35
Konza	P. Adler	plants	18
BBS	E. White	birds	20-35
Portal	E. White	mammals	25
Portal	E. White	plants	14
NTL	D. Balsiger	fish	22
NTL	D. Balsiger	phytoplankton	22
Jornada	J. Yao	plants	30+
KBS	K. Gross	plants	15
SEV	S. Collins	plants	14
GBER, Utah	R. Gill	plants	50?

Next Steps

We plan to produce at least one and perhaps as many as four manuscripts on species time relationships. We are currently collecting data sets that we will analyze and providing software to others who want to analyze their own data. The manuscript that we are sure we will complete will be a comparison of species time relationships across ecosystem types and for different taxonomic groups. The key questions will have to do with slopes and intercepts of the relationships. If data permit we will also address species time-species area interactions. We are still discussion where to send this manuscript. The leading possibilities are Ecology and BioScience. The second manuscript would be focused on the conservation implications of species time relationships. Specifically we will deal with the use of one time sampling to define biodiversity hotspots and how the results of our cross system analysis either support call into question such an approach. Subsequent manuscript(s) would deal with biodiversity management and how species time relationships may or may not complicate current approaches.

Participants:

Adler, Peter

Arkama, Katie

Colburn, Betsy

Cook, Bill

Dalgleish, Harmony

Dan Reed

Homma, Kosake

Kaufman, Dawn

Kaufman, Don

Kratz, Tim

Lauenroth, Bill

Lowe, Winsor

Lynch, Michael

Milkucki, Jill

Muldavin, Esteban

Rassweiler, Andrew

Riwa-Figura, Francisca

Schloss, Pat

Seastedt, Tim

Shecky, Yehoshua

Smith, Melinda

Vogt, Allison

Waide, Bob

White, Ethan

Yang, Xia

Yao, Jin