Week 4.1
Foraging Ecology
Why Foraging?
Definition of Heterotrophs: Animals are classified as heterotrophs because they rely on consuming organic substances for energy.
Starvation: Identified as a major cause of death in animals, motivating the necessity of foraging.
Energy Function:
Fuels biological processes essential for life.
Survival: Maintains basic internal functions and effective behaviors.
Growth and Maintenance: Involves size increase, tissue turnover, repair, and handling seasonal changes.
not just in size but our hair and nails etc.
Reproduction: Encompasses gamete production, mating efforts, and parental care.
Energy stores
left over energy if there is any
under stressful conditions we will tap into this store or if the conditions are very high and we need to expend more energy to stay alive
Energetic & nutrient content
Influence on Animal Ecology:
Foraging needs shape various aspects of ecology including:
Movement patterns
Inter-specific interactions: competition, predation, mutualism
Intra-specific interactions: territoriality, cooperation
Foraging as Necessity
Animals must forage to provide energy for:
Maintenance
Growth
Reproduction
Energy Allocation:
Follows a predictable order based on needs.
Varies annually and over the lifetime of the animal (e.g., food scarcity can enforce trade-offs in energy allocation).
Energetics 101
The relationship between energy intake and expenditure includes:
Energy from food
Acquisition/Processing Costs: Energy spent acquiring and processing food
Maintenance: Energy required for survival functions
Growth and Reproduction: Energy allocated to growing and reproductive activities.
Energy Reserves: Storing excess energy for future use.
Nutritional Aspects of Food
Energetic and Nutrient Content: Different types of food vary in energy and nutrient profiles
Proteins: Contain amino acids; crucial for tissue growth and repair; energy yield is approximately 4 kcal/g.
Carbohydrates: Include sugars and starches; used immediately or converted into fats for storage.
for immediate use… directly fuel ATP… extra carbs get turned into fat
Fats: Most efficient way to store energy, providing about 9 kcal/g.
can be consumed directly
store energy as fat bcs it is the most energy rich tissue
Fat is denser than carbohydrates, making it an ideal source for long-term energy storage and insulation.
every dietary type contains these components in dif ratios… some grass contains 15-18% crude protein, nonstructural calbs 4-5%, 30-40% structural and 2-3% fat
dif animals need dif portions and choose dietary items relative to the contribution of what they need in their diet
Example - Grass Analysis:
Fresh, new growth of Big Bluestem:
15-18% crude protein
4-5% non-structural carbohydrates
30-40% structural carbohydrates
2-3% fats.
Cost of Foraging: Search Phase
Search Time: Time taken to locate food items based on several factors:
Food type (trophic levels & abundance)
eating grass… if animal lives in native prarie then everywhere you go there is grass so you don’t have to waste time finfing food
eating grass with affids… they suck nutrients from mustard plants … cost to find food source is a sig portion of its toatl energy potion
animal sensory ability… cost of sensing and the neuro processing to distinguish it from something else
antagonism vs. mutualism in foraging
sometimes animals are eating things that Want to be eaten like when eating fruit
Animal sensory abilities
Foraging dynamics (antagonism vs. mutualism).
Types of Dietary Specializations
Frugivores and Plant Mutualists: Fruits have evolved to encourage consumption (e.g., they “want” to be eaten). animals that eat fruit are in a mutualistic relationship w the plant… animal gets energy… plant gets seed dispersal which enhances genetic diversity and can lead to the establishment of new plants in suitable habitats.
Insects and Antagonistic Predators: Utilize camouflage and defense mechanisms to avoid predation.
insects want to about being eaten
good for insectivore to eat insect but not food for insect to be eaten… this is why so many insects have camouflage and defense spikes to avoid predation
Cost of Foraging: Handling Phase
Energy Spent Handling: The time taken from locating food to fully consuming it can vary widely and includes:
Catching/acquiring food
Preparing food for consumption
Ingesting food.
Opportunity Costs: Time spent foraging that could be utilized for other activities (e.g., mating or resting).
shoebill stork live near water that is oxygen poor so the fish and animals in the water need to come up for air and once the animal comes up they try to catch which is costly and they have to aggresively wack their prey which is more of a cost and this can take up to half an hr which results in them usualy eating once a day
they aren
t able to sit on nest bcs they have to wait for food to surface
Energetics Considerations in Foraging
Endotherms vs. Ectotherms
Endotherms:
Temperature regulation consumes a significant portion of total energy budgets.
Maintaining body temperature (T_b) in cold environments requires a larger energy investment.
in the winter they have to actively regulate their bodies to be warmer and vice versa in summer when it gets too hot
Ectotherms:
Exhibit energy costs that are typically 1/10th to 1/30th of the equivalent endotherm when considering size.
Metabolic rates increase with temperature but are limited by ambient conditions.
spend way less energy to keep temp compared to endotherms which means they need a lot less to eat as temp increase the field metabolic rate decreases but as the temp goes in for ectotherms it goes up
when ectotherm body temp goes up then they are able to do more things such as forage and mate… when it gets cold their whole apparatus slows down bcs environment is responsible for metabolic rate
ecto therm when cold cant do stuff so they are only able to do everything they need to in certain times of the year
we tend to see more species richness in lizards in warmer areas and birds in cooler areas
Heterothermy
temporary reductions in body temp ~ turning down the thermostat, which can help conserve energy during extreme temperatures while still allowing for periods of activity when conditions are more favorable.
lot of dif ways to modulate that internal temp
chipmunks have
Body Size and Energetics
There is a close relationship between energy expenditure, metabolic rate, and body mass (example of allometry).
Smaller animals tend to have a higher metabolic rate relative to size, consuming more energy per unit mass (slope approximately 0.73).
small ones have relatively higher metabolic rate per unit mass… bigger animals consume a loth more energy total but use less energy per unit body mass compared to smaller animals
think abt how bison eats grass low energy and birds eat high energy fruits
humming birds forage all the time on a very high energy food source, can’t take a break bcs they’re little
consequences of body size for foraging
range of prey sizes that are acc consumed by each spider can feed on changes but the species of the prey did not change just size based on their own body size
Implications of Body Size on Foraging
Predation Dynamics:
Animals typically prey on smaller organisms.
Small animals exhibit narrower dietary ranges compared to larger animals.
Research on non-web-building spiders shows that the diversity of prey sizes increases with the body size of the predator.
Digestive Adaptations Affecting Dietary Choices
Carnivores:
Consume energy-dense, protein-rich foods
Possess short, simple digestive tracts with high efficiency (80-90% digestion).
able to extract a lot from the different food types
Represent low dietary diversity with variable gut microbiota.
prey for carniboreas contain lots of proteins and fats,
gut microbiome is tuned to the food sthat they eat
Herbivores:
Digest cellulose-rich materials with lower energy content.
Have long, complex digestive systems needing large food volumes with 40-50% digestive efficiency…. this is so they can extract as much as they can from their food since cellulose is extremely hard to digest
Host complex, stable gut microbial communities crucial for fiber breakdown.
Microbiomes and Nutrition
Gut microbiomes in both vertebrates and invertebrates play vital roles in:
Improving digestion
Detoxifying harmful substances.
Dietary Specialization vs. Generalization
Specialist Organisms:
Exhibit high efficiency in locating and digesting a select few food types.
Characterized by morphological, physiological, and sensory adaptations that enhance foraging
Competitive edge in consuming specific food resources.
often tend to be more at risk in environments that humans have messed up
Generalists:
Have a moderate capacity to forage across a wide range of prey types.
Show behavioral flexibility with higher intelligence, risk tolerance, and brain size.
can process lots of different types of food
have lots of plastisity causing them to be risk takers, higher brain size an dmore likely to iteract w humans brain tissue is very expenssive ut needed so they can really take advantage of their environment
Optimal Foraging Theory (OFT)
Predictions
Focuses on maximizing caloric intake while balancing the quality of nutrients.
Forecasts:
When resources are abundant, prioritize high-quality food types.
Include lower-quality foods when higher quality is sparse.
Case Studies
Example: Black Rhino and Greevy’s Zebra
Adjust foraging strategies based on environmental productivity; high productivity favors grass consumption over acacia.
Foraging Efficiency: Understanding Profitability
Profitability Types
Type 1 Response: Handling time either negligible or synchronized with search time.
Type 2 Response: Consumption rate decreases as prey density increases, limiting intake by processing abilities.
as density of prey increases the time they spend foraging increases which is why line flattens out
Type 3 Response: Predators struggle to locate prey at low densities but improve over time with learning.
going to grocery in a different country but going there takes longer to find what you need bcs different packaging or some things we keep in certain isle will be kept in different one is ndifferent countires…. as density of the prey increase the predator getw uses to looking and locating prey
The Marginal Value Theorem
Describes decision processes in choosing when to stay within a patch or move elsewhere based on:
The rate of energy gain per unit time in the current patch (Benefits).
Time and energy costs of moving to another patch (Costs).
Factors influencing decision-making include:
Patch quality
Distance between patches.
as resources get depleted the benefits of leaving will outweigh the cost of leaving and we need to find that
y-axis is how much energy game per time…. increases to an asymptotes w green line….when you take the distance for search and time at that patch we can find the time at which the animal should leace the patch and look for the next one
in general further patch is away the longer they will stay at the patch
how would overal reduction in patch quality affect time in patch
going to spend less time at the patch bcs the benefits of leaving will outweight the cost of leaving bcs the patch is lower quality
Coping with Foraging Scarcity
Scarcity can be seasonal or unpredictable, requiring adaptive strategies:
Movement/Migration: To areas with more abundant resources.
Cost Reduction Strategies: Lowered activity levels or thermoregulation.
Energy Storage: Harvesting food when available for future shortages.
Cost-Reduction Approaches
Short-Term Strategies: such as heterothermy or inactivity to lower energy expenditure.
Seasonal Strategies:
1) Increasing insulation.
2) Lowering metabolic rates.
3) Entering states of torpor, hibernation, or diapause.
4) Timing reproduction around periods of resource abundance.options with dealting with scarcity is to move and reduce activity cost or store energy
Internal vs. External Storage Mechanisms
Internal Storage
Importance of fat storage prior to predictable shortages. Longer-term strategies allow energy preservation.
Costs and Benefits of Internal Storage:
Benefits: Readily available energy source, protection from external threats.
Costs: Heavier body mass results in reduced mobility and increased predation risks.
most costly locomtion is flight…. for those animals theres a strong penelty for being heavier…. can’t carry around a whole bunch of weight…. ability to get away from predator is lessened when bird is heavier
heterothermy… changing the internal temperature
inactivity… spend less energy to do what needs to be done
koala take long naps and snakes chill under rocks to conserve energy
seasonally can reduce cost by decing head loss… get denser coats during winter time
can acclimate… metabolic cost of low temps…. black dot = metabolic cost of cold temp in summer but same weateher in winter isnt as metabolically costly
torpor, hibernation, diapause - dramatic reductions in metabolic rate that have huge enrgy savings
minimize shotfall during periods of the year where there isn’t m’uch to eat
coping w scarcity
internal srorage… get fat
External Storage
Caching: Hiding food supplies as a strategy to manage variable food supplies.
putting food in hiding place to cope w variable supply
hide when there is no snow then find food again when there is snow
Types of Caching:
Larder-hoarding: Store a bulk amount in one location.
Scatter-hoarding: Distributing food at multiple locations (e.g., Clark’s nutcracker remembers the positions of thousands of seeds).
Costs and Benefits of External Storage
Benefits: Little physical costs associated apart from enhanced foraging efforts.
Costs: Time spent in storage, risk of theft, and spoilage (evidence of episodic memory in scrub jays). time spend defending it
spoilage
Social and Neural Traits Associated with Caching
Scatter-Hoarders: Exhibit larger brains due to the cognitive costs of memory and navigation.
Larder-Hoarders: Often show cooperative social traits for food protection (group defenses and sometimes cooperative breeding). cant defend larder and forage food for larder at same time so groups get together and will help eachother out…. sometimes will even help out with their young
Competition in Foraging
Competition for food resources is intense during lean seasons, particularly among species with similar foraging traits:
Diet overlap.
Similar foraging space and time preferences.
Comparable body size and associated foraging morphology.
expect competition to be grater when there is less food available
Intra-specific Competition: Often leads to territorial behaviors and accounts for age- and sex-related individual differences.
Group Foraging Strategies
Cooperative Foraging:
Enhances effectiveness of hunting and resource acquisition when food requires collaboration.
Available food sources in groups reduce individual starvation risk.
Multi-species Interactions:
Minimize competition through dietary partitioning while utilizing group defense strategies.
Summary Take-Home Points
Foraging is essential for animals as it provides energy necessary for survival functions.
Energy allocation is prioritized towards maintenance, growth, reproduction, and energy reserves, shaped by ecological contexts.
Basic macromolecules have unique functions and energy content, with foods presenting variations in ratios.
Foraging costs consist of searching and handling, influenced by ecological factors including organism size and sensory abilities.
Energetics differ significantly between endotherms and ectotherms, profoundly affecting foraging strategies and distribution.
Body size plays a crucial role in determining what animals can prey upon and their foraging dynamics.
The relationship between microbiomes and dietary specialization highlights the importance of digestive adaptations across ecological niches.
The Optimal Foraging Theory provides insights into how different species adapt their diets and foraging strategies based on resource availability.
Coping mechanisms for food scarcity can involve movements, cost-reduction strategies, and varied storage methods that respond to environmental stimuli.