Transcript Slide 1
Vegetation Patterns of the Tallgrass Prairie: A Proposal Daniel McGlinn Map courtesy of PG Earls McGlinn 2005 Outline • Introduction – The Species pool hypothesis and turnover • The Tallgrass Prairie Preserve – Management methods and goals • Species-area and species-time theory • Preliminary analyses: diversity through space and time • Future Questions McGlinn 2005 Species pool hypothesis Speciation large-scale migration small-scale migration Filtering dispersal Abiotic factors and Biotic interactions Actual species pool Local species pool Regional species pool Redrawn from Zobel 1997 McGlinn 2005 Development of Species-pool hypothesis • Importance of regional species pool – Zobel 1997 • Evolutionary or historic soil conditions determine local species richness (SR) – Pärtel 2002 and Ewald 2003 • Exotics may provide key insight – Palmer 2003 McGlinn 2005 Field of Dreams hypothesis • Special case of Species-pool hypothesis – Palmer et al. 1997 • If you build it (disturbance regime), they will come… – Evolutionary pattern of burning and grazing • Predicts an increase in natives and a decrease in abundance and richness of exotics McGlinn 2005 Species pool hypothesis Speciation large-scale migration small-scale migration Filtering dispersal Abiotic factors and Biotic interactions Actual species pool Local species pool Regional species pool Redrawn from Zobel 1997 McGlinn 2005 Turnover • Species level – Carousel model: van der Maarel & Sykes 1997 – Mobility indices: Palmer and Rusch 2001 • Community level – Species-area curve: Watson 1859 – Species-time curve: Preston 1960 McGlinn 2005 Community level turnover • Species-area and species-time relationships – Preston’s (1960) ergodic conjecture – Rosenzweig 1995,1998 – Tested for time-space interaction – Adler and Lauenroth (2003) – Sampling and ecological effects – White (2004) McGlinn 2005 The Tallgrass Prairie Preserve • • • • 15,000-hectare natural area Owned by TNC since 1989 Bison introduced 1993 Randomized burning regime began 1993 • Ecological goal: – To create a heterogeneous landscape that contains the full compliment of native species McGlinn 2005 Current data • UTM grid 1997-2000 • 20 quadrats resampled 1998-2004 – Plots chosen randomly with criteria that it not have any woody cover, standing water, or >20% rock cover McGlinn 2005 10 m Map courtesy of PG Earls McGlinn 2005 Randomized Burning • Simulate the presettlement fire frequency and seasonality • Burn units selected randomly from areas with a minimum fuel load • Creates a spatially and temporally dynamic landscape McGlinn 2005 Species-area and Species-time • Structure of the equation – c, z, and w values • Empirical results – linearity and nonlinearity • Mechanisms drive patterns – Statistical, ecological, evolutionary McGlinn 2005 Structure of SAR log S log c z log A • c and z values; • c is often only interpreted as a mere intercept • Non-linear form of SAR shows that c actually helps to determine the slope S cA z McGlinn 2005 Structure of STR • Same as SAR log S log c w log T S cT w • Rate of species accumulation is w McGlinn 2005 Empirical curves from the TGPP Fig from Palmer et al. (2003) Log # Species z = 0.30 Log Area McGlinn 2005 Empirical patterns Rosenzweig 1995 McGlinn 2005 TGPP quadrat scale Preston 1960 McGlinn 2005 Current findings • Species richness has significantly increased in the twenty 10x10 plots from 1998 to 2004 • SAR is slightly convex in log-log space • STR more linear in log-log space • The rate of species-accumulation decreases at the same rate for increasing area and increasing time McGlinn 2005 McGlinn 2005 McGlinn 2005 Mean r2 = 0.9816 McGlinn 2005 Mean r2 = 0.9982 McGlinn 2005 Decreasing rate of species accumulation Slopes of species-time curves w z Slopes of species-area curves log T log A McGlinn 2005 McGlinn 2005 Remaining questions • Continue to resample plots – When does ecological change begin to take place – How does fire and grazing effect the shape of this relationship • At what scale do spatial and temporal accumulation of species seem equivalent? – Is this the same as for Konza (47 m2)? • Is the way that organisms move from one location to another analogous to their ‘movement’ through time? McGlinn 2005 Questions McGlinn 2005 Other explanations abound… • Exotics maintain or increase – A more heterogeneous landscape structurally provides more niches – Exotics are inherently generalists and can adapt rapidly to new environments – highly plastic phenotypes