Presentation on theme: "Apples and oranges How can we take the findings from a domestic situation where a cat comes home to a bowl of food to A predator that has to hunt down."— Presentation transcript:
Apples and oranges How can we take the findings from a domestic situation where a cat comes home to a bowl of food to A predator that has to hunt down its prey regardless of what species it is??? Pumas don’t normally kill adult cows, in New Mexico IF they do kill cattle it is the calves. Final from here
Why the calves? Because ranchers find it more convenient to have cows give birth in the mountains!!! Again, the root of the problem is not the predator but how humans have changed the system!!
One last word on subsidizing What ever happened to “Buffer Species”???? Remember them? Suppose to take the pressure off of a less preferred species! Didn’t fit our preconceived ideas so we changed it to subsidized, base on HOUSE CATS!!!
What do we make of all this?? Why then, do we see these effects sometimes but not others? Why do we see difference among areas. Is there something we are missing? What is being left out of all these models?? Lets revisit some of these examples to see if we can find out more.
Forty-mile herd in the Yukon 1920’s-30’s, gold miners/hunters killed tens of thousands: Overhunting but should come back! What else? Second world war, Alaska highway and other roads were built. Change of habitat!
Wildebeest of Kruger “cropping” again overhunting but before decline fires in the 1950’s’ and 60’s reduced woodland density. During 1970’s Elephants kept woodland low 1980’s poachers reduced elephants and woodland grew back. Habitat change
Pumas and big horn sheep After all is said and done, they mention: “…the encroachment of woody vegetation may increase hunting success of ambush predators like mountain lions.” Admit that there has been a change in habitat characteristics.
New one: wolves/caribou/moose British Columbia: Wolves feed on caribou, no moose historically. Moose came in since 1900’s as a result of logging practices. Habitat change
Birds “habitat fragmentation for passserine birds breeding in deciduous forests of North America is thought to be the primary reason for the major decline in their populations.” “Predation rates are inversely related to forest patch size….” Change in habitat
Differences among areas Why do we see 20 fold difference across habitats that have predators? - Habitats are different
The list goes on and on… Important reoccurring points: 1)Human disturbance: The one example where human influence is the least (Isle Royale) we see a different system.
Isle Royale 535 km 2 ; 50 wolves (93 wolves/1000 km 2 ) 800 moose (1,495 moose/1000 km 2 ) Other 56 wolves 1,495 moose Lowest Moose den Is: 1,134!
Compare that with this 93 wolves/1000 km 2 1,495 moose/1000 km 2 Where would that point fall?? Highest wolf/moose ratio ever!! Other: 56 wolves
What is going on?? Yet this system has not collapsed!!! Actually quite stable (600-2400) Remember “stable” wildebeest population: 900,000-1,300,000! Obvious wolves have not devoured all their prey! This “garden” seems to be doing fine even with the “weeds”
What is different?? Human influence minimal: National Park What are we missing??? What is being left out of the equations?? What is the one thing we identify as being the most important in wildlife management?? Habitat!!!
Second commonality Not just human interference per se What are they disturbing/changing?? In all cases either changed the habitat somehow or in the case of the caribou comparison, was comparing different habitats that had different densities.
Have they totally left it out? Might be too harsh on reductionists K was meant to reflect what the habitat could support: “natural limit of a population set by resources in a particular environment.” The Rosenzweig and MacArthur model tries to incorporate it somewhat. But just a varying K
Population ecologist’s view In this scheme, the important aspect of the environment or habitat is its sum or average, not its makeup or variance So, more ignored that climate is the actual “playing field” where predator-prey interactions are carried out!! Add that to this….
Ecologist’s view of predation One ball killing another, the end!
No wonder we have problems! By stripping off the behavior of animals and the variability of habitat, we may be able to get to the “roots” of scientific principles but they will be devoid of any realism. Thus producing the conflicting results we see and the extreme level of confusion
What do we need to do? To try and make sense of all this we need to evaluate what role habitat plays in the predator prey relationship. We then have to see if this helps us explain more than what we can now. Hopefully this will give us a better understanding of the role of predator-prey relationships in ecosystems AND how to manage them!!. here
How does habitat make a difference Habitat is probably THE most important aspect of wildlife ecology and management but yet we often give it lip service only. So lets start with the basics. What is habitat? Suite of resources (food, shelter) and environmental conditions (abiotic and biotic) that determine the presence, survival, and reproduction of a population.
Base problem One of the basic problems is in the definition “Suite of resources…..” Talks about sum and total, not its makeup, often assume uniformity. Habitat in an area is not uniform so we need to look at the makeup of the habitat and the juxtaposition of its elements.
Landscape view Need to look at habitat on a landscape level. Landscape ecology does this and is where the composition of habitat elements become important. No time for landscape course but will look at elements that are important regarding predator-prey.
First off, prey Had said that patch characteristics, quality, size, shape, location were important in adaptive foraging strategies. Here we are equating patch to landscape element. Also mentioned that predation risk was considered relative to patch use. Would only consider it IF it differed among patches
So basics Landscape elements or patches vary across home range of an animal. Vary in forage quality, predation risk, and use for missed opportunity activities.
So “habitat” looks not like this but more like this
Each patch has its own characteristics AND the composition of these patches CHANGES from home range to home range and on a larger scale!
Result? Result of this is that indeed each animal faces different possibilities and limitations on how it can use its home range. On a larger scale, whole populations face different combinations. Obviously affects foraging strategies but can also affect population dynamics.
Simplest Size and number of food resource patches gives us those different values of K that give us so much trouble. But they also affect the predator-prey relationships No wonder we get different results. Like doing “parallel” experiments under totally different conditions: one green house in the sun and other in the shade!
Habitat differences make a difference!! To understand how habitat makes a difference in predator prey relations, we need to first… Look at the predator’s landscape.
A predator and its landscape Predator also has to look for food –found in “resource patches” However, unlike herbivores, food moves AND does not like to be eaten! So, as we saw earlier, need to incorporate not just abundance or availability of prey but their catchability. This varies across habitat types!!
Need to talk about lethality So unlike prey where how much you eat depends on how fast you can bite and chew or how rich the food patch is, a predator has to be able to catch its food. Predator lethality: basically how efficient it is in catching a prey. If your good, your lethal, if not…. What is predator efficiency? Here
Predator efficiency Definition: # successful captures/total attempts Difficult to quantify in the wild Rarely ranges over 30% Average probably around 20% Is quite variable
Reasons for variability? Health of prey: Young, sick, and old more vulnerable so hunting efficiency would be higher for these groups Mid-aged healthy prey can defend themselves But their ability to do so varies with habitat
Habitat and predator efficiency Each predator has strengths/weaknesses Wolves: Adapted to run prey down, attack from behind.
Patch quality for predator So high quality patches for predators are ones where they have a good chance of making a kill. How important is this to the predator? Presentation on edge effects
The landscape of opportunity So through the eyes of the predator, the landscape is one of a mixture of successful and less successful patches.
Return to our habitat patches Now each has a success value to it for predator. Based on lethality of predator.
How about the prey? It is within this framework of predator lethality that the prey must make their foraging decisions! So…. Becomes not as simple as selecting the patch with the highest food resources. Need to balance food resources and predation risk.
Which is more important? In the past, placed most (if not all) emphasis on resource levels (remember K again). How long does it take to starve? How long does it take to get killed by a predator? Food is important but not if your dead!
Predation risk So the risk of being killed (predation risk) becomes overlying factor in how a prey will use the habitat. What are its options? 1) use dangerous areas less/safe ones more 2) If you have to go, spend little time/use vigilance to offset dangers/reduces feeding efficiency here
Two principle lines of investigation 1. Changes in habitat 2. Changes in the amount of vigilance.
Where risk is high: - Use the most secure areas Where risk is low: - Use all parts of habitat
2. Changes in Behavior. -Time foraging vs surveying.
Where risk is low: - eat more and survey less. Where the risk is high: - survey more and eat less.
Since the 1980’s – lots of studies: Mech, L.D. 1977. Wolf-pack buffer zones as prey reservoirs. Science 198:320-321. Edwards, J. 1983. Diet shifts in moose due to predator avoidance. Oecologia 60:185-189. Stephens, P.W. and R.O. Peterson. 1984. Wolf-avoidence strategies of moose. Holarctic Ecology 7:239-244. Hunter, L.T.B. and J.D. Skinner. 1998. Vigilance behaviour in African ungulates: the role of predation pressure. Behaviour. 135:195-211. Scrimegeour G.J. and J.M. Culp. 1994. Foraging and evading predators: the effect of predator species on a behavioural trade-off by a lotic mayfly. Oikos 69:71-79. And more.…
All indicate that the prey are adjusting their behavior because of the risk of predation.
So what do we have? Predator that has varying lethality Prey that responds to this by avoiding high risk/lethal areas
All this made us think of what might be the basic force to explain these reactions of prey to their predators.
as they move about the landscape to reduce predation risk. Fear of predation changes how they use the landscape
is seen through their eyes as a landscape of differing levels of risk or fear Thus a landscape of physical features Or
We chose the concept of fear because. We know it is an emotion that exists on the intra specific level (complement agression!).
If a subordinate animal can show fear of its superior. Imagine what its emotion would be when faced with a predator that is going to kill it!
Flip side of landscape of Opportunity So predators look at landscape relative to opportunities Prey look at it relative to fear! Evidence that prey respond to this: use safe areas more than risky one. Lets return to the predator:
What should a predator do? Conventional wisdom: predator should hunt where there is the most prey. Landscape of fear/opportunity: why should predator hunt were it is the most difficult to catch its prey? Maybe conventional wisdom is not so wise??
Add the two together How should predator and prey concurrently use habitat?
Space use race Andy Sih in the 1980’s proposed the concept of a behavioral response race. Prey should avoid predators and if can, will be more prevalent where there are low predator #. Landscape of fear model predicts the same.
Predator? Behavioral space race predicts predator should actually hunt where there are less prey! Landscape of fear/opportunity predicts the same.
So what do we have? Two player game: prey trying not to be eaten Predator trying to eat! We should see a separation of the two over the landscape, prey using safer areas more, predators using areas of less prey but where they are more lethal. Evidence for this? presentation here
Summary Habitat MAKES a difference! Non-lethal effects may be more important to wildlife management than lethal ones. May be able to manage impact of predation via habitat. Landscape of fear/opportunity may be the most valuable management tool in management AND conservation. Example?? Go to sheep presentation here