Two species use the same limited resource or harm one another while seeking a resource Resource Organisms use common resources that are in short supply Resource Interference Interference Organisms seeking a resource harm one another in the process, even if resource is not in short supply Long history in ecology Competitive exclusion principle: Complete competitors cannot coexist Leads to specialization N. American ungulates tend to be generalists flexible in habitat use and feeding? Page 66, Bailey 1984 Why? Pleistocene extinction 12,000 15,000 years ago most large mammals went extinct.. 1
Would you expect competition among these species? Page 66 from Bailey 1984 Which ones and under what conditions? Even though species occupy different niches, enough overlap for competition Contemporary examples? How would you know if competition is occurring? Tables 1 and 2 from Henke et al. JWM 52:595-598 Examine diet overlap Study of ungulates in the Texas Hill Country Another way is to look at several niche dimensions. If a lot of overlap, then competition is possible. Isle and Hellgren 1995 J. Mammalogy 76:784-799 Bedding sites also different Pigs bedded on edge of mottes with better visibility Peccaries bedded in thick vegetation with low visibility 2
On Chaparral WMA (JWM 65:99-110) Pigs used more open areas; less selective in placement of HR because HR was large Peccaries favored dense woody vegetation and were more selective in HR placement understood best through manipulative experiments Expensive to conduct, will see data later Pigs used open areas, peccaries used thick vegetation with more cactus Temporal day vs. night habitat use Livestock Wildlife?? Livestock Wildlife Important because both wildlife and livestock have value that people wish to capture Different from wildlife--wildlife Livestock densities above sustainable Not subject to density dependent controls Artificial feed, water and removed if range conditions become bad Impacts of livestock on wildlife Direct resource and interference competition that we have discussed Indirect (esp. if grazing pressure is high) Reduction in plant vigor Lower reproduction by plants Changes in vegetation cover types Changes in plant species composition Change habitat use & movements of wildlife Operational impacts Species of livestock Grazing regime (timing and duration) Fencing Water development Range alteration (e.g. brush control) Predator-prey relations altered Disturbance from management activity Disease 3
White-tailed deer in general Least likely to compete with cattle Compete with sheep for forbs Compete with goats for browse Wet years deer preferred cattle > goats > sheep Dry years deer preferred cattle > sheep > goats Avoided pastures w/ livestock Survival and natality lower w/ livestock Study of cattle-deer competition in western Colorado (Ecological Applications 6:200-227) Elk winter ground, cattle summer grazing Positive effects of elk Removed dead grass, cattle diets better quality Negative effects of elk Forage biomass was reduced Higher diet quality was not enough to make up for reduced intake rate Lower calf production in pastures grazed by elk Dead grass was important as a buffer in this arid system Elk grazing reduced this buffer Lessons for wildlife management: Well managed grazing may serve as a tool in deer management by removing grass and promoting growth of forbs In Great Basin, livestock grazing reduced fires and promoted shrub growth. Benefited mule deer whose populations increased through the mid 1900s Intraspecies competition? Males and females live in different habitats or use habitats differently. Why?? Predators? Avoid competition? Different food quality requirements? Sexual Segregation Larger-bodied males eat abundant, high-fiber forage Rumen capacity = prolongs retention time Able to use fiber for energy Females smaller-bodied, but requirements change Better post-rumen digestion and nutrient absorption Digestive tract changes Barboza and Bowyer 2000 4
Views of predators have changed Considered competitors & dangerous Early form of game management Military shot predators in YNP soon after it was established 1930s different view emerges Leopold watches wolf die Errington proposes doomed surplus Predators in South Texas Original predators: Wolves Lions Jaguars Bears Coyotes Bobcat And people! Now. Timing of fawn deaths What kind of coyote predation rates have been reported? 18.0% 27.6% 16 19.4% 27.0% 10.3% 12.7% 1.9% 12.0% 4.3% 18 73.0% 20.4% 24.7% 14 47.9% 54.0% 7 28% 59.2% 23.3% Vreeland (2002) 218 fawns effects are complex Predators limit prey in some situations How can we determine predator effects? Mortality sources Manipulated systems Manipulative studies 5
Figs. 1 and 2 from JWM 38:857 Welder Refuge: coyotes & bobcats 361 ha enclosure for 7 years Lions S Texas: 49% (37 of 75) lion kills = deer 58 bucks marked near Freer in late 80 s 15 deaths 2 killed by lions Bobcats Scats at Welder Deer hair May-Aug, peaks in June Adult deer rarely taken Coyotes 81 fawns collared in 60 s 58 died, 29 = coyote Freer study, 58 adult bucks 3 deaths where coyote was probable Heffelfinger study, 3 yrs, 97 bucks 8 deaths, 3 where blood, signs of struggle 6
Vulnerability of prey Habitat quality Animal quality Poor quality animals more susceptible to predation Buffer species Predator evasion strategy Not effective against all predators Predators are part of the system So what s the bottom line Role of predators not appreciated until recently Consider Aldo Leopold s changing views on wolves and predators in general You must consider coyote predation in the context of your deer herd conditions! In productive deer herds, coyote predation may not be a significant factor So what s the bottom line In low-productivity herds, coyote predation may limit the number of does that can be harvested. Either must increase productivity, or reduce mortality (control?). How to limit coyote predation? Consider the habitat Cover! 7
South Texas is a place of contrasts South Texas is a place of contrasts Grazing management = cover management Grazing management = cover management Rain: the great equalizer Abundant forage for lactating does Plenty of cover for fawns 8
Drought: the real fawn-killer Poor forage for lactating does Little cover for fawns Fewer buffer species Supplemental Feeding: the Other Equalizer Help even out drought effects Increase deer visibility Increase individual productivity Fawns/doe Body or antler size Increase density (more deer) not always a good thing! Expensive, but effective in arid region Flexibility: adjust grazing for drought Wolves and bears controlled in Alaska and Yukon to benefit moose populations Use this manipulation to study predation effects Bears and wolves near carrying capacity Moose densities avg=148/1000km 2 (range 45-417) Bears and wolves below carrying capacity Moose densities avg=663/1000km 2 (range 169-1447) 4 factors influence effect on prey Ratio of predators to prey Vulnerability of prey Changes in predator behavior Density independent factors Ratio of predators to prey Higher ratio predators likely to limit prey species 1 wolf:200 caribou is stable 1 wolf:20 moose is stable 9
Fig. 31-7 from text book Ratio of predators to prey Numerical response of predators More deer = more food more coyotes (or wolves, etc.)?? Prey diversity Alternative prey could remove numerical response. Many small mammals may allow coyote populations to remain high, even if deer decrease Ratio of predators to prey R values, longevity of prey and predators Predators lower reproductive rates and higher survival rates than prey Fig.1 JWM 65:19-24 Predator swamping When prey is vulnerable, have many individuals to limit predator impact Caribou calves Ratio of predators to prey Geographic concentrations of predators Garbage dumps and bears Intrinsic regulation of predators Territoriality could limit predator numerical response Predator behavior Concentration of predation Success causes predators to focus effort Predator learning Experience more effective techniques Predator group facilitation Groups of predators more successful than single predator (e.g. wolf packs) 10
Predator behavior Concentration of predator effort (e.g. lynx eat fewer caribou calves when hares are abundant) Density independent processes Weather or habitat changes can influence all these factors, but not related to prey density 11