This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. ViabilityAnalysis in Biological Evaluations:Concepts of PopulationViability Analysis, BiologicalPopulation, and EcologicalScale LEONARD F. RUGGIERO GREGORY D. HAYWARD JOHN R. SQUIRES RockyMountain Forest and Range ExperimentStation 222 South 22nd Street Laramie,WY 82070, U.S.A. Abstract:Environmental protection strategies often rely on Analisisde viabilidaden evaluaciones biologicas: Conceptos environmentalimpact assessments. As part of theassessment del analisisde viabilidadpoblacional, poblaciones biologicas process biologistsare routinelyasked to evaluate theeffects y escala ecologica of managementactions on plants and animals. This evalu- ation oftenrequires that biologists make judgments about Resumen: Las estrategiasde las agencias deproteccion am- the viability of affectedpopulations. However,population biental se basanfrecuentementeen las evaluaciones del im- viability analyses that are analytically comprehensivere- pacto ambiental. Como parte del proceso de evaluacion, se quire extensiveecological data. Such data are usually un- pide rutinariamentea los biologos que evalu'enlos efectosde available and impossiblefor wildlife managers to collect acciones de manejo sobreplantas y animales. Esta evalua- given limitations of time and money. In this paper we cion requiere frecuentementeque los bi6logos juzguen present a conceptual framework to help managers assess acerca de la viabilidad de las poblaciones afectadas. Sin population viabilitygiven thereality of limitedinformation embargo, los anaclisis de viabilidad poblacional que son and resources.Our framework includes a series of steps that analiticamentecomprensivos requieren datos biologicos ex- facilitateassessment of managementimpacts on population tensivos.Tales datos no estan usualmente disponiblesy son viabilitywhile stressingthe importanceof reconcilingdis- imposiblesde colectarpara los administradoresde vida sil- parities between the geographic scale of management ac- vestredebido a las limitacionesde tiempoy dinero.En este tions and thescale of ecological responses.We argue thata trabajo nosotrospresentamos un encuadre conceptualpara gross mismatchof scale betweenlocal managementactions ayudar a los administradoresa evaluar la viabilidad de las (e.g, timbersales) and geographicallyextensive ecological poblaciones en vista de la realidad de las limitaciones de responses (e.g., species viability) reduces the reliability of informaciony recursos.Nuestro encuadre incluye una serie environmentalanalyses. Ourframeworkstresses "biological de pasos que facilitan la evaluacion de los impactos del populations" as the most appropriatelevel of ecological or- manefosobre la viabilidad depoblaciones mientrasque en- ganization for conductingimpact analyses. We argue thatin fatiza la importanciade reconciliarlas disparidades entrela most cases environmentalanalyses of local management escala geograficade las acciones de manejoy la escala de las actions should assess theecological responsesofpopulations respuestasecol6gicas. Nosotrossostenemos que un desajus- ratherthan the responsesof entirespecies, as is now com- tecrasode la escala entreacciones de manejo local (e.g venta monly the case. We also present ecological concepts that de madera) y respuestasecol6gicas geograficamenteexten- sivas (e.g viabilidad de especies) reduce la confiabilidad del Paper submittedAugust 3, 1993; revisedmanuscript acceptedJanu- anaclisisambiental. Nuestroencuadre enfatiza a las 'pobla- ary 19, 1994. ciones biol6gicas" como el nivel ma's apropriado de orga- 364 ConservationBiology, Pages 364-372 Volume 8, No. 2, June 1994 Ruggieroetal. ViabilityAnalysis 365 have been used effectivelyby biologistsin makingjudgments nizacion ecologica para conducir el anaclisis del impacto. about management effectsand in developing conservation Nosotros mantenemos que en la myoria de los casos, el plans. Although not completelygeneralizable we believe anaclisisambiental de acciones de manefo locales deberia theseconcepts, summarized from the conservationbiology evaluar las respuestasecol6gicas de las poblaciones antes literature,can aid in evaluating population viability:(1) que las respuestasde la especie en su totalidad, como es connected habitats are betterthan disjointed habitats; (2) actualmenteel caso. Nosotrostambien presentamos concep- suitable habitats in closeproximity to one anotherare better tos ecologicos que han sido usados efectivamentepor bio- than widely separated habitats; (3) late stages offorest de- logos en el juzgamiento de los efectosdel manejo y en el velopmentare often betterthan younger stages; (4) larger desarrollo de planes de conservacion. Creemos que si bien habitat areas are betterthan smaller areas; (5) populations estos conceptos,resumidos de la literaturade conservacion with higherreproductive rates are more secure than those biologica, no son completametnegeneralizables, pueden with lower reproductiverates; and (6) environmentalcon- ayudar a evaluar la viabilidad poblacional: 1) haibitats ditions thatreduce carrying capacity or increase variance in conectadosson mejoresque haibitatsinconnexos; 2) habitats thegrowth rates ofpopulations decreasepersistence proba- apropiados cercanos entresi son mejoresque habitats sepa- bilities. radospor grandesdistancias; 3) estadios tardiosde desarro- llo forestal son usualmente meforesque estadios ma's jo- venes; 4) acreasde hacbitatsmas grandes son mejores que areas mas pequenias;5) poblaciones con tasas reproductivas mas altas son mas seguras que aquellas con tasas reproduc- tivas mas bajas; y 6) condiciones ambientales que reduzcan la capacidad de carga o incrementenla varianza en las tasas de reproduccionde las poblaciones disminuyenla probabi- lidad de persistencia Introduction ical Evaluationor other impact analysisnecessarily in- volves some kindof population viability analysis (PVA). Currentenvironmental protection strategies rely heav- Gilpin and Soule (1986) described PVA as a complex ily on environmentalanalyses. Environmental analyses process of consideringall factorsthat affectthe pro- are intendedto supportdecision-making processes by cesses ofspecies extinction.In a formalPVA (one thatis evaluatingthe potentialenvironmental effects of alter- analyticallycomprehensive) it is necessaryto integrate nativemanagement actions. For example,federal regu- thosefactors that influence the likelihoodof extinction, lations and agencypolicy stemmingfrom the National such as demographic,genetic, and environmentalsto- EnvironmentalPolicy Act (NEPA) and the NationalFor- chasticity,as well as lifehistory and habitat-useparam- est ManagementAct (NFMA) requireU.S. ForestService eters. In addition,basic ecological processes like dis- biologiststo evaluate whetheror not managementac- persal, competition,and predation also need to be tions contributeto the loss of species' viabilityon Na- understoodas theyinfluence population persistence. In tional Forest lands. Species classifiedas threatenedor otherwords, a formalPVA (whether qualitative or quan- endangeredunder the EndangeredSpecies Act and spe- titative)is comprehensiveand requiresconsidering the cies classifiedas "sensitive"by the NationalForest Sys- entiretyof a species' (or population's) ecology. In for- tem are oftenemphasized in environmentalanalyses. mal PVAsecological relationshipsand demographicpa- One specific type of environmentalanalysis con- rametersare often incorporatedinto a mathematical ducted by Forest Service biologists is the Biological model thathelps predictpopulation trends and extinc- Evaluation.Biological Evaluations are usuallydirected at tion probabilities. the effectsof individual management actions (e.g., a spe- Appreciatingthe complexityinvolved in the PVApro- cific timbersale) on plantsand animalsthat occur on a cess is usefulbecause it servesas a measureof our gen- managementsite. In Biological Evaluationsbiologists eral ecological understandingfor a given species. But mustprovide written documentation of their judgments when biologistsare routinelyrequired to make judg- about whetheror not a proposed managementaction mentsabout population viability with extremely limited will increase the likelihoodof sensitivespecies becom- data and resources,they face numerous professional and ing threatenedor endangered.Accordingly, the Biolog- personal difficulties.In thispaper we hope to aid biol- ical Evaluationprocess providesimportant information ogistsfaced with conducting viability analyses when lo- to decision makers,and biologistsare held accountable cal demographic,habitat use, and life historydata are fortheir judgments. These judgmentsare formalizedin unavailable. "determinationof effect"documents. To make viabilityassessments more practicalfor re- The basis forthe determinationof effectin a Biolog- source managers,wTe discuss the basic characteristicsof ConservationBiology Volume 8, No. 2, June 1994 366 ViabilityAnalysis Ruggieroet al. PVAand attemptto dispel the theoreticalmystique sur- This emphasison persistenceleads us to focuson the roundingPVA by placing the concept in a practical criticalimportance of time and changingenvironmental framework.We also presenta discussionof "biological conditionsover time (Ruggiero et al. 1988). Viability populations"and "ecological scale," concepts we feel assessmentsmust address both populationpersistence must be carefullyaddressed for meaningfulimpact as- withinacceptable habitatand