10. Heterotrophs & Energy

Lecture 10

Herbivores vs Carnivores vs Detritivores

^^Herbivores^^ → organisms that **eat plants**

^^Carnivores^^ → organisms that **eat animals**

^^Detritivores^^ → organisms that **eat nonliving** (dead) **organic matter**

Food Economics Scale

Need to balance **ease** of getting food (**E used**) & food **quality** (**E gained**)

Scale w an **inverse relationship** → inc. ease = dec. quality (& vice versa)

Define: Ecological Stoichiometry

**Balance** of multiple **chemical** elements in **ecological interactions**

Eg. trophic levels

Ecological Stoichiometry:

Relative Abundance of Carbon & Nitrogen (C:N ratio)

**Varies** → dictates what/how each time of heterotroph eats

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^^Plants^^ → **high C:N** → lots of C used to build up structure

^^Animals, fungi, bacteria^^ → **low C:N** → less C needed

What are the five elements that primarily make up biomass?

How does each contribute?

^^Carbon^^ → provides **structure** to organisms → major building block of all living things

^^Oxygen^^ → part of **water** molecules

^^Hydrogen^^ → part of **water** molecules

^^Nitrogen^^ → part of **amino** & **nucleic acids**

^^Phosphorus^^ → essential for **cellular processes** → ex. ATP E transfer

Herbivory:

Economic Tradeoff

**High** ease (E used) → **lower** quality (E gained)

B/c **high C** & **low N**

Herbivory:

Nutritional Chemistry & Plant Defense Challenges

(4)

**Low [N]** but high \[C\] → **low nutrient** content

**Cellulose** & **lignin** → strengthen plant tissues but inc. C:N & are difficult to ingest/digest → need adaptations to consume

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Plant **physical** (eg. spines, thorns) &/or **chemical** (eg. toxins) **defenses** to overcome in order to consume

Herbivory:

Ease of Acquiring & Quality of Food

Type of Adaptation Common to Herbivores

^^Ease^^ → generally **easy to find** & less competition

^^Quality^^ → plants are **poor food** → animals must **consume large amounts** to satisfy

\
Adaptations → **digestive**

Carnivory:

Economic Tradeoff

**Low** ease (E used) → **higher** quality (E gained)

**Higher** energetic **cost**/harder to obtain but is **nutrient rich**

Carnivory:

Economic Stoichiometry Among Prey & Impact on Predator

Relatively **constant C:N** ration across animals species → **many prey** species available to predators b/c all nutritionally similar → can have a more **varied diet**

Carnivory:

Action of Selection & Type of Adaptation

Selection is **stronger** on the **ability** & **efficiency** of **capturing/consuming** diff preys → weaker on nutritional requirements

Adaptation → help them to **hunt effectively**

Detritivores vs Decomposers

^^Both^^ → contribute to decomposition → play essential role in **nutrient cycling**/recycling

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^^Detritivores^^ → must **ingest** & **digest** dead organic matter via **internal** processes

^^Decomposers^^ → can **directly abs.** nutrients through **chemical** & **biological** processes

Detritivory:

Economic Tradeoff

**High** ease (E used) → **higher/lower** quality (E gained)

Easily available but most nutrients have already been abs or lost

Detritivory:

Ecological Stoichiometry of Most Dominant Food Source

Food source → **dead plant material**

Are **rich** in **carbon** & **energy**, but are **poor** in **nitrogen** →

N is often limiting in live plants so there’s a selection for inc. N Use Efficiency which **reabsorbs N before** dropping leaves → now **even less N** for detritivores

Detritivory:

Limitations

^^Not limited^^ by **food** → relatively **high abundance** of dead plants in most communities

^^Limiting factors^^ → **abiotic** factors & **chemical composition** of food have more direct impacts

Omnivores vs Mixotrophs

Some organisms exploit **more than one** carbon source.

^^Omnivores^^ → gain E from both **plant** & **animal** matter

^^Mixotrophs^^ → can gain E from **photosynthesis** (inorganic) & from **consuming** organic materials

What are the heterotrophic plants?

(2)

^^Saprophyte^^ → obtain **food** from **dead matter** → lack chlorophyll → no photosynthesis → heterotroph

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^^Parasites^^ → obtain **food** from **living plant host** → poor in chlorophyll → limited photosynthesis → most nutrients from the host → heterotroph

Plants that appear heterotrophic but aren’t

(2)

^^Epiphytes^^ → grow on other plants but **don’t parasitize** them

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^^Insectivorous plants^^ → obtain **additional** nutrients from **trapped insects** → prefer photosynthesis but will eat insects → are **mixotrophs**

Define: Functional Response

The **relationship** b/w **food availability** (density) & **feeding rate** (intake)

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**Inc.** in **feeding** rate → eventually **levels off** in response to an **inc.** in food **availability**

Factors Influencing Feeding Rate

(5)

1. How much can **physically fit** in their mouth
2. **Time** to **digest** food → room for more
3. **Time** to **find** food
4. **Time** to **handle/process** food
5. Sometimes it’s **safer to hide** than to eat

What is displayed on functional response curves?

What is ILC on these graphs?

**Food intake** x **time to look for food**

^^ILC^^ → incipient limiting concentration → **prey density** at which **food intake** **levels** off into **asymptote**

Type I Functional Response Curves

(3)

Feeding rate **inc. linearly** (b/c of quick food processing) up to an **ILC**

At ILC → feeding rates **level off abruptly** → reaches its **max feeding rate**

Only animals requiring little/no time to process food have curves like this → eg. filter feeder

Type II Functional Response Curves

(3)

Feeding rate **inc. linearly** at **low** conc. → **slower** rate at **moderate** conc. → then **levels** off at **high** conc.

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Limited by **food search** at **lower** densities

Limited by **processing** & **digestion** at **higher** densities → food is widely available

Type III Functional Response Curves

(2)

Feeding rates are ^^S-shaped^^ → **low** at **low** densities → **inc.** greatly at **intermediate** densities → then **levels** off at **high** food densities

Can sometimes be seen when → food is better protected, uncommon food is ignored, inexperience hunting it, or starving animals

Optimal Foraging Theory

(4)

Describes how organisms feed as an **optimizing process** → by **maximizing** or **minimizing** some factors

Attempts to explain __what/when/where__ animals will eat

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Assumes that if **E supplies** are **limited** → organisms **can’t max all** of its life fxns at once → must **allocate** E

**Cost/benefit** of allocating E to feeding

Marginal Value Theorem

(2)

Describes the **optimal time** for a forager to **move** from one food patch to a **new location**

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First reaches patch → consumption rates at **max** b/c there will be lots of food remaining

As food consumed → rate of intake **slows** b/c longer to find remaining food

What does the optimal time to leave depend on in marginal value theorem?

(3)

1. **Time** to **move** to a new patch
2. **Qualities** of a patch
3. Aspects of the **foraging environment**

A → energy gain per unit time

B → total energy gained by an organism as it forages in a patch

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C → **maximizes energy** gain **per** unit of **time**

D → red

E → blue

Interpret Formula for Energy Intake of Predators

^^E^^ → energy

^^T^^ → time

^^Ne1^^ → number of prey encountered /unit time

^^Cs^^ → energy expended (cost) searching for prey

^^H1^^ → handling time

Diet Composition:

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How does the energy intake equation predict how many prey species a predator will prey on?

Whichever (E/T) is greater will be favoured

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**One** prey species if → eq. **one** prey **>** eq. **two** prey

**Two** prey species if → eq. **one** prey **