COYOTE POPULATION PROCESSES REVISITED

It appears that coyote (Canrs latrans) abundance 1s determined pr~mal-~ly b avallabil~ty of food (prey) as mediated through social dominance h~erarchles and a telritol-ial land tenure system. This is reflected in rates of reproduction, dispersal, and mo~tality, with survival ofjuveniles a major factor Suggestions for a new gencrat~on of simulation niodels to explore coyote population funct~ons are included l'opulatio~i manipulation is a prominent component of many coyote management programs. Understand~ng the factors affecting animal abundance and the mechanisms of populat~on regulation can sss~st In recognizing the merits and liabilities associated w ~ t h such management approaches. In tuni, this should help identify more flexible management scenarios and result in management programs that are more selective, effect~ve and efliclent. Gier (1968) and Knowlton (1972) prov~ded some ln~tlal ~llforn~ation on coyote populat~on parameters. Additional info~~nat~on fr m a variety of authors lcad Knowlton and Stoddall (1983) to hypotlies~ze that coyote abundance was governed by interactions between ava~lable food (prey) and coyote behav~oral charactel-~st~cs, namely soc~al dominance and territoriality, with the impact expressed through the processes of reproduction, mortal~ty, ingress and egress. S~milar conclusions were reached by Packard and Mech (1983) to esplaln population regulation in grey \valves (C. Ilcpl~s). Hel.ein we revlew these ideas in I~glit of infornlat~on acquo-ed In recent years Evidence concerning footl abundance K~iowlton and Stoddart (1983) used 3 llnes of ev~dence to support the contention that food abundance was a major detelminant of coyote abundance, namely (I) state by state averages of the ~ndices of coyote abundance calculated from the Westwide Survey of Predator Abundance (1,lnhal-t and Knowlton 1975, Roughton and Swecny 1982), (2) a meager data set concelnlng coyote and rodent abundance on s~ tcs cattered throughout Texas, and (3) a 1 5-year time serles of coyote and jack]-abbit (Lepus cul,Sot~riicl~s) density est~mates In Curlew Valley, Utah Since the prevlous paper, the data set for the iirst has not changed and pnor ~nterpretations remain largcly Intact, I.e., mean coyote abundancc varies among the westcm states and appears to reflect pnrnruy productivity H~gher dens~ties occur in the Great Plains, a relat~ve scarcity typ~fies the mte~mou~ta~ii reglon, and moderate abundanccs are found among the states of the Pacific coast. In add~tlon, an Increasing kline In dens~ty from northern to southern states seems ev~dent This appears conslstent w~th observations by Weaver (1979) and Todd and Kcith (1 976) suggest~ng food suppl~es in wulter may be part~cularly important in areas where cond~t~ons are more harsh Gese (1995) identified available food resoul-ces in w~nter to be pa~ticularly ~rnpol-tant in replating size of coyote packs In Yellowstone National Park The second data set, conceinlng the relative abundance of coyotes and rodents on s~tes throughout Texas has not been elaborated and is unconvlnclng on ~ t s own Nowevcr, the results are conslstent w ~ t h other sources of information Slncc the earher paper, annual and semi-annual density est~mates for coyotes and jackrabb~ts in Curlew Valley, Utah, were extended to 28 years . Ihat data sct includes intb~mat~on I dicating the u~-upt~on I jackrabbit numbers that peaked In 1980 subs~ded to vely low nun~bel-s by the mid-1 980s and was ~ollowed by another inuption in the early 1990s Coyote numbers, however, did not follow the an~lcipated patterns. When jackrabbit numbers dccllned in the mid1980s, coyote numbers remained h ~ g h Faced with explaining deviance from the cspected, 2 hypotheses were identified The first suggest~iig this resulted from a marked mcrease in the abundance of deer and antelope in Curlew Valley, pi-ovtd~ng an alternate winter food resource. The other hypothes~s involved lower mortality rates associated with reduced hunian exploitation result~ng 6-om lower fur pnces and a reduction in the ~ntensity of esploitat~on to protect domest~c stock. Although our current preference resides w ~ t h the first alternative and 1s conwstent with the food abundance hypothesis, no addit~onal data have been assembled to clarify the issues. On the other hand, Hamlin et al (1 989) reported that during a population decline of mule deer (Odocoileus hettriontts) In north-central Montana, coyotcs remained abundant. They hypothesized that coyote sul-v~val may have increased as a result of Increased abundance of microtme I-dents as an alternative food source. This was unlikely In Cui-lew Valley because m~ci-otines are not common (I-Iol'fiiian 1979). Othastudies have added to our understandings A companion study to the Curlew Valley research involved inonitoring rodent, lagomo~ph, and coyote populat~ons over a 12-yeaiperiod on the Idaho Nat~onal Engtneering Laboratoiy (INEL), a slte some 100 nl~les north of Curlew Valley and largely linrnune from puhlic access (Stoddart 1987). Data from this location are slmilar to those fi-om Curlew Valley, \vlth jackrahb~t populat~ons inupt~ng from exvemely low numbers In the late 1970s to over 280 per mi2 In 198 1 , and then returning to very low levels by the m ~ d 1980s Co~ncident w ~ t h the increase In hares, coyote abundance Increased 5fold, followed by a gradual decllne dter hares became scarce. This re~nfoi-ces previous interpretat~ons about the potential role of prey abundance In detennin~ng coyote abundance. One notable aspect of the INEL data is the relatively slo\v response In coyote abundance to the ab~upt decl~ne in a major food resource Two years after the jackrabb~t population I-etuined to vely low levels, the sprlng coyote dens~ty index was still 3 times pre-~n-uption levels. Todd et al. (1981) and Todd and Ke~th (1983) found that wlnter coyote abundance was ~II-ecily related to snowshoe hai-e abundance In their study, all demographic pal-anieters of coyotes measured declined as snocvshoe hares became scarce, leading them to bel~cve that lo\v ava~labll~ty of alternate prey In the boreal forest ~ntlrnately linked the coyote pollulat~on to tluctuat~ons in sno\\ishoe hare abundance. Based on an I l -yea]study in southel-n Texas, Windherg (1 995) prov~dcd data iiid~cat~ng coyote population growth was correlated positively with wlnter prey abundance and con-elated negatively w ~ t h ~n~ t i a l coyote abundance Since both prey and coyotcs were extremely abundant in the area (spring coyote populations estimated at 4-7 per mi2), the coyote population may have been approach~ng the upper lim~ts for density and other constraints may have also been operating This study is particularly notable in that ~t documents a negative relationsh~p between coyote abundance and populat~on growth. Although convict~ons that a relat~onsh~p between coyote abundance and prey abundance have been I-emforced in recent yeai-s, more definitive understandings of that relationship have not emerged Improved quantitative assessments of the abundance and availability of prey in relat~on to coyote density, along with the adoption of standardized methodology among studies are needed to provide more enlightenment. Long-term monlto~mg of predator and prey populations will be essential to clariry the Impacts and mechanism(s) link~ng predator and prey populations