Vocabulary:

• Predator: an organism that consumes another organism
• Prey: an organism that is consumed by a predator
• Carnivore: an organism that consumes animal tissue
• Herbivore: an organism that consumes plant or fungal tissue
• Omnivore: an organism that consumes both plant and animal tissues
• True Predators: predators that directly hunt and kill their prey
• Planktivore: true predators that specialize in consuming plankton
• Lotka-Volterra Model: a mathematic and/or graphical representation of predator prey relationships, that assumes that the consumption of a prey species by a predator (and the predator population’s resulting size) is directly correlated with abundance of the prey species in the habitat
• Optimal Foraging Theory: foraging strategies minimize the energy spent to acquire resources, and maximize the energy gained from those resources
• Red Queen Hypothesis: refers to the constant “evolutionary arms race” between predators and prey
• Mullerian Mimicry: unrelated species share a similar coloration to amplify the visible signal of a trait (e.g., toxicity)
• Batesian Mimicry: harmless species mimic deadly ones
• Parasite: an organism that takes nutrients and energy from another living organism (call the host), but does not kill them. Parasites typically associate with their host for an extended period of time.
• Parasitoid: an organism that takes nutrients and energy from another living organism, eventually killing their host
• Mesopredator: mid level predator species that is preyed upon by the apex predator, while simultaneously preying upon species at lower trophic levels

Outline of Notes:

Types of Predation:

Predation can be divided into different categories based on what an animal eats and how it acquires its food.

• Predation can be separated into three broad categories based on diet:

1. 1. Carnivores: Consume animal flesh
   2. Herbivores: Consume plant or fungal tissues
   3. Omnivores: Consume both animals and plant/fungal tissues

• Predation can also be categorized by how they acquire their prey:
  • True predators: Hunt and kill prey directly
    • Differ from herbivorous “predators” which eat a lot of abundant food at one time and do not necessarily kill the plant. However, animals that eat seeds cause immediate mortality as they would otherwise be able to germinate.
  • Planktivores: True predators that specialize in feeding on plankton.
    • Considered true predators as they consume the entire prey item
  • Parasites: take nutrients and energy from another living organism (host) with whom they are closely associated, for an extended period of time but do not kill them.
    • Not true predators as they need their “prey” to survive in order for them to remain alive.
  • Parasitoids: take nutrients and energy from another living organism, eventually killing their host.
    • Not true predators as they do not kill the host immediately

Modeling Predator/Prey Interactions:

• Lotka-Volterra Model: Models predator/prey interactions. Assumes that the consumption of a prey species by a predator is directly correlated to the abundance of the prey species in the habitat.
  • I.e. there is a lag in the predator populations in response to the cyclic peaks of prey.
    
    
• Do predator/prey cycles actually exist or is it a product of mathematical modeling?
  • Natural heterogeneity in the environment allows for recovery of prey as well as predator populations, which shows the cyclical nature of these dynamics.
  • The greater number of prey, the more the predators can eat.
• Three types of consumption curves:
  • Type 1: Linear; predators consume the same proportion of prey, regardless of prey abundance
    • Ex: Filter feeders
  • Type 2: Linear in a decreasing fashion then reaches a plateau; predation declines as prey abundance increases  
    • Ex: Lynx
    • Most common type of consumption curve
  • Type 3: Sigmoidal curve that reaches an asymptote; highest rate of predation at intermediate proportions of prey abundance
    • Ex: Crabs
    • Also prey switching when prey becomes too sparse so buffer foods are consumed.

Predator Responses:

• Predators respond to prey availability functionally and numerically:
• Functional response: relationship between the rate of consumption and the number of prey available
  • Increased prey abundance = increased predator consumption
• Numerical response: relationship between the rate of consumption and the number of predators in an area
  • Increased consumption = increased predator populations
  • Predator populations can increase via reproduction and immigration
• Game Theory/Optimal Foraging Theory: time and energy are considered in foraging
  • Natural selection favors efficient foragers:
    • Maximum energy or nutrient intake per unit of effort
    • Minimize time/energy spent foraging  
  • Factors to consider:
    • Type of prey item
    • How to search for prey
    • Location and amount of time spent searching
  • Ex: Pied wagtails preferred medium-sized prey because it maximized calories and minimized time spent eating

Avoiding Predation:

• Coevolution involves 2 “players” (species, male and females, 1 species and ecosystem, etc) in relationship; both are constantly changing in response to the other’s changes
• Red Queen Hypothesis: constant evolution and adaptation is needed for a species to maintain its fitness relative to the other species or systems it is interacting with
  • Examples: colors, camouflage, venom, poison immunity, etc
• How do prey species avoid predation?
  • Two main defense categories:

1. 1. 1. Induced: brought on by predators

• • • • Ex: Behavioral defenses

1. 1. 2. Constitutive: permanent fixed features

• • • • Ex: Camouflage, mimicry, protective armor, satiation of predators (mass emergence of cicadas)
        • Mullerian Mimicry: Unrelated species share a similar coloration → amplifies signal
        • Batesian Mimicry: Harmless species mimic deadly ones

• How do plants avoid predation?
  • Structural Defenses:
    • Ex: thorns, shells, trichomes
      • Picture 
  • Chemical Defenses:
    • Active inhibitors: chemical compounds released in response to damage, functioning as a cry for help (induced)
    • Quantitative inhibitors: a compound produced in large quantities
      • Ex: tannins, fiber, resins
    • Phytoestrogens: chemicals that disrupt reproduction
    • Qualitative inhibitors: small amount will substantially affect predator
      • Ex: nicotine, caffeine, spicy compounds
  • Relationships with animals that protect the plant
    • Ex: bullet ants protect host tree

Interactions Between Plants, Herbivores, and Carnivores:

Plant, herbivore, and carnivore densities all interact and affect one another.

• Predators influence prey dynamics by inducing morphological, behavioral, and physiological defense responses.

• Herbivore costs of avoiding predation:
  • Loss of feeding opportunities
  • Reduced foraging time and food intake
  • Delayed growth/development
  • Decreased population size

 Blog-Style Summary:

When you think of predation, you probably imagine lots of different things, maybe it’s wolves eating rabbits or sharks eating fish, but there are many ways that predation occurs in the ecological world. Starting with the basics, a predator is an organism that feeds on and consumes other organisms. But what types of predators are there? Predators can be defined by the type of prey that they consume. Carnivores are organisms that consume animal tissue, such as tigers (seen in figure 4). Herbivores consume plant or fungal tissue, like rabbits (seen in figure 5). It may seem shocking that herbivores are considered predators, but believe it or not they are since plants are still considered prey items! Lastly, we’ve got omnivores, which are organisms that consume both plant and animal tissue, and a classic example is the grizzly bear (Ursus arctos horribilis) (seen in figure 6).

 But what makes a predator a “true predator”? Usually, the traits that determine what a true predator is are whether or not they kill their prey immediately and consume them entirely. So species that are grazers, browsers, or scavengers (feeding on part of each victim without actually killing it outright), parasites (feed on their host while it’s still alive and are not immediately lethal), or parasitoids (take a long time to kill their prey) don’t fit this definition and are therefore not considered true predators! Just to solidify this concept, let’s go over some examples of what would be considered a true predator. Seedivores, or animals that consume seeds, are considered true predators; their ‘prey’ is entirely consumed and (most of the time) does not survive being eaten. An example of this is a black-capped chickadee (Poecile atricapillus) eating a sunflower seed. Another category of true predators includes planktivores, which are species that consume zooplankton and/or phytoplankton. An example of a planktivore is a whale shark (Rhincodon typus); this species eats its prey by opening its large mouth and slowly swimming through swarms of plankton on the ocean’s surface (Seen in Figure 7).

        Predators can respond to prey availability in two ways: functionally, through their rate of consumption, and numerically, through their change in population densities. If prey densities are high, a predator’s rate of consumption will increase (functional response) and their reproductive rates will increase, increasing predator populations (numerical response). In order to understand these complex predator-prey interactions and their effects on the species involved, we often look to the Lotka-Volterra Model
(See figure 8). We use this model to consider the population dynamics of two different species at the same time. Following the trends of the chart, predator populations lag behind the population peaks of prey. It can be important to consider this model when predicting the effects of one species on another. For example, if lions completely disappeared from the Serenegeti, how may this affect Thomson’s gazelle populations? The answers to these questions are more easily predicted using the Lotka-Volterra model, which can give indications of species population health. Many factors influence control of prey populations by predators; this includes availability of cover for prey to hide, choice of multiple prey species, prey scarcity and evolutionary changes in predator and prey species.

This model is a good basic example of how predator and prey populations play off each other, but some scientists in the past have questioned how accurate it is in the years after it was created. In one study, headed by C.F. Gauss, the “predator lags behind prey” dynamic was only seen when predators and prey were added to already existing populations in his tests. But this study was really simple, and one by C.B. Huffaker took these tests to the next level. Huffager studied orange mites, and after setting up his experiment… they were all killed by predation. However, when partitions and shade were added to allow prey to hide, the Lotka-Volterra model predictions were observed (Figure 9)!  Having areas for prey to hide (but also areas where they can be caught) was the key. The Lotka-Volterra model isn’t just purely mathematical – it’s been proven to exist in the field.

 So when predators aren’t eating their prey, what are they doing? At some point, they need to increase their population size! Predators do this through reproduction and aggregation, which is the collection of predators coming together through immigration. When predators are searching for prey, they must sacrifice time and energy. According to the Optimal Foraging Theory, or Game Theory, predators must utilize their limited time and energy as efficiently as possible to survive. Therefore, natural selection favors efficient foragers; predators must maximize the energy/nutrient intake per unit of effort, and minimize the time and energy spent on foraging. An example of an efficient forager includes the pied wagtail (Motacilla alba), which prefers medium-sized prey species to minimize handling time and maximize caloric intake (Figure 10).

        Considering how complicated predation is, it’s no surprise that it has effects on conservation. When conserving true predators or prey species, the dynamics of predation are always important to consider. Giving predators access to prey usually isn’t enough. In some species, like the African Wild Dog (Lycaon pictus) (Figure 11), prey needs to be available for them to eat, but not so much that lions and hyenas begin to frequent the area, since they will chase the dogs away from their prey in order to scavenge it for themselves (Creel, 2001).

Looking at predation and our ‘true predators’, we can see just how important predation is, especially in environments where we find intraguild predation, when natural competing predators prey upon one another while simultaneously preying upon other species in the area. This type of scenario leads to areas that are bound to have mesopredators as well. Mesopredators are the mid level predators that are preyed upon by the top level predator, while simultaneously preying upon the lower level species. Mesopredator issues arise in environments where the top level predators are removed by natural or human causes. The absence of top level predators will lead to a major increase in the mid level predators, to the point of an overabundance. (Muller & Brodeur, 2002). Through a classic snowball effect, we will be left with a diminishing population of prey species, and an overpopulation of these mesopredators. Along with this, we can look at areas where there is a lack of predator species altogether. Certain residential areas that contain an overpopulation of white-tailed deer see a major increase in vehicle collisions. When you add in predators, deer populations will even back out and deer collisions become much less of an issue. Overall, we can see that predator-prey relationships can be a very complicated thing to look at. There are many factors that contribute to the abundance of both, as well as many factors that contribute to the overall health of an ecosystem. Predation is a key factor in ecosystem health, and is something that is absolutely necessary to promote positive conservation practices.

 Spotlight on NC:

Did you know that on your drive to the popular vacation spot, the Outer Banks, you can hear the wild howls of “America’s wolf”? Red wolves (Canis rufus) are an historically important predator, which means they consume other organisms, known as prey. More specifically, they are carnivores, meaning they consume animal tissue. They commonly hunt rabbits, raccoons, mice, nutria, and white-tailed deer [1]. Their history in America and more specifically, North Carolina is complicated and their role as wild predators is an important conservation issue.

Early in America’s history, red wolves were hunted and killed by European settlers due to fearful and competitive attitudes that drove predator eradication programs. By the 1960s, only a few were left in the wild in Texas and Louisiana, and 17 pure red wolves were identified to begin a captive-breeding program. This unique species was considered extinct in the wild in 1980 with barely over 60 in captivity, but a wild population was established in 1987 by the U.S. Fish and Wildlife Service (USFWS) [2]. The USFWS chose the North Carolina coast, specifically Alligator River and Pocosin Lakes National Wildlife Refuges, to establish this managed population because it already had large amounts of protected land, was less developed, and coyotes had not expanded into that area at the time. This landscape is a productive natural system with a notable amount of biodiversity and differing landscape types such as agricultural, developed, undeveloped, and state/federal land [2]. Additionally, this region is an ecologically unique area with swamps, forests, coastal prairies and rare pocosins which provides varying habitat and resources for the wolves [1].

The population of red wolves established in the National Wildlife Refuges is considered a nonessential-experimental population (NEP) under Section 10 of the Endangered Species Act, which is a legal term that means that the individuals that are released are protected and if they are not successful we would not lose valuable genetics. In the early 2000s, the number of estimated wild red wolves was believed to be 130, which is when the North Carolina population peaked. Since then, there has been a notable, slow decline in the population size [2]. Human interactions, like gunshot mortality and vehicle strikes, coyote hybridization, and program changes by the USFWS have affected the trajectory of population recovery of the red wolf [1, 2]. Currently, wild red wolf populations are estimated to be around 20 individuals.

Red wolves act as a control agent for the prey populations in their territory. They especially regulate deer and “nuisance” populations, such as raccoons and nutria, which prevents them from destroying cropland and other human resources [1]. They are true predators that hunt and kill their prey immediately upon capture. White-tailed deer consist of over half their diet and are important prey species to the wolves. A further breakdown of the composition of the red wolf diet can be seen in Table 1, and shows their unique ecological role in NC food webs [3].

Wolf consumption of deer is extremely important for population control. Because deer are herbivores, meaning they consume plant or algal tissue, the overpopulation of white-tailed deer in the absence of wolves in North Carolina has led to ecological problems such as the overgrazing of vegetation. Overpopulation has also led to increased negative human-wildlife interactions such as vehicle strikes, and negative impacts on other small mammal species. The removal of native predators, namely the red wolf, that regulate these populations has caused populations to skyrocket. With the rise of diseases in prey species, such as Chronic Wasting Disease, the re-establishment of natural predators is extremely important to recover and improve native ecosystems in North Carolina [4]. 

Red wolves also consume other herbivores and prevent their populations from growing too large and consuming all of the nutrients available in the ecosystem. Red wolves influence prey dynamics in their region by influencing prey defense responses, and a lack of these natural predators can fundamentally change the behaviors and landscape interactions of these prey species. Predator-prey dynamics, when there are enough of each species for this to be significant, allows each to regulate the other’s population with both numerical (increasing rate of prey consumption leads to increased predator population) and functional responses (the rate of consumption based on the number of prey). However, due to their current population sizes being so low and very high mortality rates, the red wolves are not able to increase their population size to fully follow a predator-prey model. There are no other populations for individuals to aggregate, or immigrate, from and although there have been some pups born there is an unfortunate lack of breeding pairs.

The conservation and management of red wolves provides a unique reminder of how human disturbance and habitat fragmentation impacts the fields of ecology, biology, and conservation. As biodiversity levels continue to decline and as urbanization and habitat fragmentation continues to increase around the globe, protecting and understanding predators, like the red wolf, will become increasingly important. Predators heavily influence their surrounding natural systems (even your nearby environment!) and their ecological roles are undoubtedly important. Restoring this NC predator could help re-introduce a healthy predator-prey dynamic as well. Public education on the importance of predators to natural systems and the beneficial role they often play for humans is vital to continue conservation efforts.

Featured Ecologists:

Corina Newsome

Corina Newsome studied the impacts of predation and climate change on where seaside sparrows choose to locate their nests, how distributed their populations are, and how successful their populations are. Climate change has caused increased sea level rises, leading to more often flooding within marshes–the seaside sparrows primary nesting environment. This increased flooding causes the sparrows to nest on higher elevations, as shown in the middle of the Biorender. However, nesting at this height increases the risk of predation due to less vegetative cover. Sometimes these marsh habitats are located near roads, causing nesting sites to be on roadsides. These areas experience less flooding due to a further distance from the marsh wetlands or rivers, however, they experience increased predation due to ample access for predators like raccoons. In Corina’s research, they discovered that despite nesting on higher land or near roadsides increasing predation, seaside sparrows often pick this risk over the risk of nest flooding from lower elevations. Therefore, edge habitats created from sea level rising due to climate change have more of an impact on seaside sparrow nesting sites and fitness than predation. This study relates heavily to our topics of predation and habitat fragmentation, and how those relationships impact the overall fitness of a species. Although this study did not agree with the original hypothesis, it is still useful information that can be used in future predation management considerations.

Terrie M. Williams, Phd

Dr. Williams’ research focuses on the physiology of large predators and how it relates to human physiology. Her lab, Williams ICE (Integrative Carnivore EcoPhysiology) Lab at University of California, Santa Cruz studies the relationship between humans, animals, and their environment to understand physiological adaptations. Her work relates to what we have studied in class about adaptations and evolution. One of Dr. Williams’ studies took place in Antarctica, where her team is researching Weddell seals and how they may follow magnetic fields underwater. The goal of this study was to understand how the Weddell seals are able to return to the same ice hole after hunting underwater hundreds of meters below the surface and in the darkness of winter. They hypothesized that the seals have a sort of “sixth sense” that allows them to follow magnetic fields. Her team studied this by using specially designed cameras that they attached to the top of the seals’ heads which recorded their underwater activity and tracked multiple factors. They found that the swimming behavior of the seals resembled the pattern of homing pigeons that flew around magnetic lines. This is really interesting because it is the first evidence of a marine mammal following magnetic lines. Dr. Williams also has a book titled “The Odyssey of KP2” about her fight to save the endangered Hawaiian monk seal.

Nyeema Harris, PhD

Dr. Harris broadly studies carnivore movement, distribution, and interactions with humans. She is interested in how the presence of apex predators affects the behavior and distribution of mesopredators, and how human presence can induce similar fear-based behavioral responses in wildlife species.

Yannis Papastamatiou, Phd

Dr. Papastamatiou focuses on shark behavior ecology by using tagging technology on a range of sharks such as oceanic whitetips and reef sharks. He also studies predator ecology which entails focusing on what drives species habitat selection and movement, studying the physiology of digestion in sharks, and how fish transfer nutrients across habitats. To study predator ecology he uses a variety of methods such as chemical tracers, multi-sensor data loggers, telemetry, videos, stable isotope analysis, stomach content analysis, and biologgers. Dr. Papastamatiou looks for the answers to what drives predator-prey relationships and looks to conserve sharks through their research and aiding in the reduction of shark fin trade. Not only does he focus on predator-prey relationships but also overall shark behavior and distribution, for example, he is studying the ability of elasmobranchs to reproduce asexually in the wild through DNA analysis. This research would be used for shark conservation to help improve management strategies of threatened shark and ray species and ecosystems. Recently he has discovered that some shark species have long-term social bonds. Dr. Papastamatiou has been on National Geographic, BBC, and Discovery’s Shark Week to display his research on shark ecology.

Student Contributors:

Note Outline: Annika Preheim, Davis Grubb, Jared Lamb, Tommy Fairbairn, Katherine Abbott

Blog Style Summary: Lauren Willhite, Molly Niekamp, Evan Storie, Ally Peters

Spotlight on NC: Rhianna Klewin, Ren Rooney, Rachel Weaver

Featured Ecologists: Sydney Beck, Mayla Ngo, Lucie Ciccone, Alana Brown