Abstract

My goal is to apply some of the tools of evolutionary biology to the Conservation of desert rivers and streams. Many of the fish and invertebrates native to desert rivers and streams possess spectacular adaptations for surviving the extreme floods and droughts that occurred before dams, irrigation, and groundwater depletion tamed these waters. Restoring extreme flows could provide a selective "sieve" that eliminates invasive non-native taxa while allowing natives to persist. The difficult question is, how much of the natural flow regime must be restored to accomplish this? That's what I propose to tackle. In many lotic ecosystems, particularly those in southwestern deserts, alteration of natural flow regimes is facilitating the replacement of native taxa by non-natives. Because native taxa often possess adaptations for surviving the extreme floods and droughts that historically occurred in desert rivers, natural flow regimes are being partially restored to favor native communities. Few attempts are being made, however, to predict the effects of these restored flow regimes on more than a few target species, although life history data are available for many invertebrates, fish, and anurans. This leaves a number of uncertainties for managers. How can antagonistic management plans be avoided, where a restored flow regime favors one native taxon but harms others? Because of practical constraints, what is the minimum amount of natural flow regime that must be restored to remove the most destructive non-native invertebrates, fish, and anurans? Which components of the natural flow regime (frequency, timing, magnitude, rate of change, and duration of floods and droughts) play the most critical roles in favoring native over non-native communities? To address these questions I will model how prospective restored flow regimes will affect the invertebrates, fish, and anurans inhabiting desert rivers. The model will combine historic data characterizing natural flow regimes (specified by time-specific dynamical equations) with life history data (contained in Leslie matrices) for both native and non-native taxa. Although this modeling approach is not as fine-grained as site- or taxon-specific models, it can be used to identify flow regimes that have promising community-wide benefits or antagonistic side effects. I will calibrate the model using taxa that occur in free-flowing rivers (San Pedro and Hassayampa Rivers - TNC preserves), and apply the results to adjacent dammed rivers (Gila and Agua Fria Rivers) to design flow regimes that differentially favor native over non-native communities.

Publications

Lytle, D. A. 2003.Reconstructing long-term flood regimes with rainfall data: effects of flood timing on caddisfly populations. Southwestern Naturalist 48(1): 36-42.

Lytle, D. A. 2002. Flash floods and aquatic insect life-history evolution: evaluation of multiple models. Ecology 83(2): 370-385. * winner of the H.B.N. Hynes Award

Lytle, D. A. 2001.Convergent growth regulation in arthropods: biological fact or statistical artifact? Oecologia 128(1): 56-61.

Lytle, D. A. 2001. Disturbance regimes and life history evolution. American Naturalist 157(5): 525-536.

Lytle, D. A. and B. L. Peckarsky. 2001. Spatial and temporal impacts of a diesel fuel spill on stream invertebrates. Freshwater Biology 46: 693-704.

Lytle, D. A. & D. Merritt. In review. Hydrologic regimes and riparian forests: a structured population model for Populus.

Lytle, D. A. & R. L. Smith. In review. Exaptation and flash flood escape.

Lytle, D. A. & N. L. Poff. In prep. Adaptation to natural flow regimes.